Surgical Trajectory Monitoring System and Related Methods

ABSTRACT

Systems and methods for determining a desired trajectory and/or monitoring the trajectory of surgical instruments and/or implants in any number of surgical procedures, such as (but not limited to) spinal surgery, including (but not limited to) ensuring proper placement of pedicle screws during pedicle fixation procedures and ensuring proper trajectory during the establishment of an operative corridor to a spinal target site.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/301,233, filed on Jun. 3, 2009 (now issued as U.S. Pat. No.8,442,621), which was the national stage entry of PCT/US07/11962, filedon May 17, 2007, which claims priority to U.S. Provisional PatentApplication Ser. No. 60/801,488, entitled “Pedicle Access Probe andRelated Methods,” and filed on May 17, 2006; U.S. Provisional PatentApplication Ser. No. 60/918,955, entitled “Trajectory Aligned PedicleAccess,” and filed on Mar. 19, 2007; U.S. Provisional Patent ApplicationSer. No. 60/919,049, entitled “System and Methods for Orienting aFluoroscope,” and filed on Mar. 19, 2007; and U.S. Provisional PatentApplication Ser. No. 60/925,630, entitled “Surgical Access System andMethods for Orienting the Same,” and filed on Apr. 20, 2007; the entirecontents of each of the above noted applications are expresslyincorporated by reference into this disclosure as if they were set forthin their entireties herein.

BACKGROUND OF THE INVENTION

I. Field of the Invention

The present invention relates generally to determining a desiredtrajectory and/or monitoring the trajectory of surgical instruments andimplants and, more particularly, doing so during spinal surgery,including but not limited to ensuring proper placement of pedicle screwsduring pedicle fixation procedures and ensuring proper trajectory duringthe establishment of an operative corridor to a spinal target site.

II. Discussion of the Art

Determining the optimal or desired trajectory for surgical instrumentsand/or implants and monitoring the trajectory of surgical instrumentsand/or implants during surgery have presented challenges to surgeonssince the inception of surgery itself. One example is pedicle fixation,which is frequently performed during spinal fusions and other proceduresdesigned to stabilize or support one or more spine segments. Pediclefixation entails securing bone anchors (e.g. pedicle screws) through thepedicles and into the vertebral bodies of the vertebrae to be fixed orstabilized. Rods or other connectors are used to link adjacent pediclescrews and thus fix or stabilize the vertebrae relative to each other. Amajor challenge facing the surgeon during pedicle fixation is implantingthe pedicle screws without breaching, cracking, or otherwisecompromising the pedicle wall, which may easily occur if the screw isnot properly aligned with the pedicle axis. If the pedicle (or morespecifically, the cortex of the medial wall, lateral wall, superior walland/or inferior wall) is breached, cracked, or otherwise compromised,the patient may experience pain and/or neurologic deficit due tounwanted contact between the pedicle screw and delicate neuralstructures, such as the spinal cord or exiting nerve roots, which lie inclose proximity to the pedicle. A misplaced pedicle screw oftennecessitates revision surgery, which is disadvantageously painful forthe patient and costly, both in terms of recovery time andhospitalization.

The present invention is aimed primarily at eliminating or at leastreducing the challenge associated with determining the optimal ordesired trajectory for surgical instruments and/or implants andmonitoring the trajectory of surgical instruments and/or implants duringsurgery.

SUMMARY OF THE INVENTION

The present invention facilitates the safe and reproducible use ofsurgical instruments and/or implants by providing the ability todetermine the optimal or desired trajectory for surgical instrumentsand/or implants and monitor the trajectory of surgical instrumentsand/or implants during surgery. By way of example only, the presentinvention may be used to ensure safe and reproducible pedicle screwplacement by monitoring the axial trajectory of surgical instrumentsused during pilot hole formation and/or screw insertion.Neurophysiologic monitoring may also be carried out during pilot holeformation and/or screw insertion. It is expressly noted that in additionto its uses in pedicle screw placement, the present invention issuitable for use in any number of additional surgical procedures wherethe angular orientation or trajectory of instrumentation and/or implantsand/or instrumentation is important, including but not limited togeneral (non-spine) orthopedics and non-pedicular based spine proceduresIt will be appreciated then that while the surgical instruments aregenerally described below as pedicle access tools, cannulas, retractorassemblies, and imaging systems (e.g. C-arms), various other surgicalinstruments (e.g. drills, screw drivers, taps, etc. . . . ) may besubstituted depending on the surgical procedure being performed and/orthe needs of the surgeon.

A surgical trajectory system may include an angle-measuring device(hereafter “tilt sensor”) and a feedback device. The tilt sensormeasures its angular orientation with respect to a reference axis (suchas, for example, “vertical” or “gravity”) and the feedback device maydisplay or otherwise communicate the measurements. Because the tiltsensor is attached to a surgical instrument the angular orientation ofthe instrument, may be determined as well, enabling the surgeon toposition and maintain the instrument along a desired trajectory duringuse.

The tilt sensor may include a sensor package enclosed within a housing.The housing is coupled to or formed as part of a universal clip toattach the tilt sensor to a surgical instrument. The sensor package maycomprise a 2-axis accelerometer which measures its angular orientationin each of a sagittal and transverse plane with respect to the actingdirection of gravity. The sagittal orientation corresponds to acranial-caudal angle and the transverse orientation corresponds to amedial-lateral angle. The sensor package is preferably situated suchthat when the tilt sensor is perpendicular to the direction of gravity,the inclinometer registers a zero angle in both the sagittal andtransverse planes. Thus, when the tilt sensor is fixed perpendicularlyto the longitudinal axis of the surgical instrument, the angularorientation of the longitudinal axis of the instrument is determinedrelative to gravity. Alternatively, a 3-axis sensor may be used. The3-axis sensor may comprise a 2-axis accelerometer to measure sagittaland transverse orientation and either a gyroscope and/or one or moremagnetometers (e.g. a single 3-axis magnetometer or a combination of a1-axis magnetometer and a 2-axis magnetometer) to measure thelongitudinal axial rotation of the instrument.

A universal clip may be provided to attach the tilt sensor to thesurgical instrument. The universal clip comprises a fastener, whichsecurely holds a surgical instrument to the clip, a sensor bed, whichsnugly holds the tilt sensor to the clip, a coupler, which connects thesensor bed to the fastener, and a collar, which travels along thecoupler to engage the surgical instrument with the fastener.

A surgical instrument for use with the surgical trajectory system maycomprise, by way of example only, a pedicle access probe. The instrumentmay generally comprise a probe member having a longitudinal axis and ahandle. The probe member may be embodied in any variety ofconfigurations that can be inserted through an operating corridor to apedicle target site and bore, pierce, or otherwise dislodge and/orimpact bone to form a pilot hole for pedicle screw placement. The probemember may be composed of any material suitable for surgical use andstrong enough to impact bone to form a pilot hole. In one embodiment,the material may be capable of conducting an electric current signal toallow for the use of neurophysiologic monitoring.

The handle may be permanently or removably attached to the probe memberand may be shaped and dimensioned in any of a number of suitablevariations to assist in manipulating the probe member. In someembodiments, the handle includes a cutout region for accommodatingattachment of the universal clip. In other embodiments, the handleincludes an integral cavity for receiving the tilt sensor directly. Instill other embodiments the tilt sensor is permanently integrated intothe instrument handle.

A feedback device may be communicatively linked to the tilt sensor via ahard wire or wireless technology. The feedback device may communicateany of numerical, graphical, and audiofeedback corresponding to theorientation of the tilt sensor in the sagittal plane (cranial-caudalangle) and in the transverse plane (medial-lateral angle). Themedial-lateral and cranial-caudal angle readouts may be displayedsimultaneously and continuously while the tilt sensor is in use, or anyother variation thereof (e.g. individually and/or intermittently). Thefeedback device may be placed next to the patient on the surgical table,or it may be affixed to any number of suitable objects in the operatingroom. Alternatively, a display may be provided that may be positioned inthe practitioner's field of view during surgery. By way of example only,the display may be attached to one of the surgical instrument, theuniversal clip, and the practitioner's hand.

A bubble level device may be provided with the surgical trajectorysystem and used to ensure the tilt sensor is functioning correctly. Thebubble level device comprises a handle with a bulls-eye level mounted init. When the handle is placed on a flat surface with the tilt sensorinserted into it, an indicator ring should encircle a bubble capturedwithin the glass. When the bubble is within the indicator ring, the tiltsensor display should read approximately zero-degrees for both thecranial-caudal and medial-lateral angle readouts.

In general, to orient and maintain the surgical instrument along adesired trajectory during pilot hole formation, the surgical instrumentis advanced to the pedicle (through any of open, mini-open, orpercutaneous access) while oriented in the zero-angle position. Theinstrument is then angulated in the sagittal plane until the propercranial-caudal angle is reached. Maintaining the proper cranial-caudalangle, the surgical instrument may then be angulated in the transverseplane until the proper medial-lateral angle is attained. Once thefeedback device indicates that both the medial-lateral and cranialcaudal angles are matched correctly, the instrument may be advanced intothe pedicle to form the pilot hole, monitoring the angular trajectory ofthe instrument until the hole formation is complete.

Before the pilot hole is formed, the desired angular trajectory (e.g.the cranial-caudal angle and the medial-lateral angle) must first bedetermined. Preoperative superior view MRI or CAT scan images are usedto determine the medial-lateral angle. A reference line is drawn throughthe center of the vertebral body and a trajectory line is then drawnfrom a central position in the pedicle to an anterior point of thevertebral body. The resulting angle between the trajectory line and thereference line is the desired medial-lateral angle to be used in formingthe pilot hole.

The cranial-caudal angle may be determined using an intraoperativelateral fluoroscopy image incorporating a vertical reference line.Again, a trajectory line is drawn from the pedicle nucleus to ananterior point of the vertebral body. The resulting angle between thetrajectory line and the vertical reference line is the desiredcranial-caudal angle to be used in forming the pilot hole. A protractoroutfitted with a tilt sensor may be provided to assist in determiningthe cranial-caudal angle in the operating room. Alternatively, thecranial-caudal angle may be calculated preoperatively using imagingtechniques that provide a lateral view of the spine. The medial-lateraland cranial-caudal angles should be determined for each pedicle that isto receive a pedicle screw. Alternate and/or additional methods forpredetermining the pedicle angles are also contemplated and may be usedwithout deviating from the scope of the present invention.

An alternate feedback device may be provided which can communicativelylink multiple tilt sensors at once. Preferably, the alternate feedbackdevice may be linked to three tilt sensors simultaneously, and anglemeasurement feedback may be provided simultaneously for all attachedtilt sensors. In one example, this allows a tilt sensor to be engagedwith a surgical instrument, a protractor, and a C-arm fluoroscopewithout the need for multiple displays and/or connecting anddisconnecting the tilt sensor to the various devices during theprocedure.

According to one embodiment of the present invention, a coupler may beprovided to attach the tilt sensor to a standard C-arm. The couplercomprises a sensor bed which receives and holds the tilt sensor, and amount which may attach to the C-arm. The sensor bed may be pivotallyattached to the mount and may preferably pivot between a horizontalposition and a vertical position with respect to the mount. This allowsthe tilt sensor to be aligned in the same starting orientation withrespect the direction of gravity whether the C-arm is in the A/Pposition or the lateral position. It will be appreciated however thatthis is not always necessary, as in some instances (such as whendetermining the cranial-caudal angle using the C-arm) the sensor outputis adequate if only one axis of the sensor is perpendicular to gravity.

A coupler may be configured to attach to the C-arm via a belt, strap,Velcro, tape, etc. . . . The coupler may be configured to attach to thesidewall of the C-arm, the face of the C-arm, or any other part of theC-arm. The coupler may also include a reticle/plumb line. The plumb linemay comprise a radio-dense marker which will appear on theflouro-images. The plumb line may be oriented parallel to the directionof gravity to serve as a vertical reference line in the flouro-images.The radio dense marker may be configured in any number of arrangementsto provide additional markings on the flouro-images. A target may alsobe provided to augment the plumb line.

In an alternate embodiment of the present invention, it is contemplatedthat the orientation of C-arm with respect to the patient may beadjusted by moving the patient rather than the C-arm. To accomplishthis, by way of example only, a tilt sensor may be attached to thesurgical table and the table may be adjusted rather than the C-arm. Instill another embodiment, a tilt sensor may be attached directly to thepatient and again, the table may be adjusted rather than the C-arm.

In addition to facilitating adjustments to a C-arm orientation, a C-armequipped with the orientation system of the present invention may haveother uses as well. By way of example only, the C-arm may be used todetermine a pedicle axis and/or a starting point for pediclepenetration.

The cranial-caudal angle may be determined intraoperatively with a C-armfluoroscope equipped with the orientation system of the presentinvention. The C-arm is oriented in a lateral position and then radiallyrotated until a vertical reference line is parallel to the pedicle axis,this is the trajectory lateral position. The angle measured by the tiltsensor is the cranial-caudal angle of the pedicle axis.

To select a starting point for pedicle penetration, the C-arm may beplaced in the trajectory lateral position. From the trajectory lateralposition the C-arm may be rotated back to the A/P position whilemaintaining the radial rotation imparted to achieve the trajectorylateral position. A surgical instrument may be advanced to the targetsite and positioned on the lateral margin of the pedicle, the preferredstarting point according to this example. The depth of penetration ofthe surgical instrument may be checked during advancement by rotatingthe C-arm back to a trajectory lateral view.

Alternatively, the starting point may be determined using an “owls eye”view. The C-arm may be oriented such that it is aligned with both themedial-lateral and cranial-caudal angles as discussed above. The tip ofthe pedicle access instrument is placed on the skin so that the tip islocated in the center of the pedicle of interest on the fluoro-image;and thereafter the instrument is advanced to the pedicle. Anotherflouro-image is taken to verify that the tip of the instrument is stillaligned in the center of the pedicle.

Using the “owls eye” view, a standard surgical instrument may be guidedalong a pedicle axis without the use of an additional tilt sensor on thesurgical instrument. In the “owls eye” image, a surgical instrumentproperly aligned with the pedicle axis will appear as a black dot. Oncealigned, the surgical instrument may be advanced through the pediclewhile ensuring that it continues to appear as only a dot on thefluoroscopy image. The depth of penetration may again be checked with atrajectory lateral image.

The surgical trajectory system may also be utilized a surgical accesssystem. Using the surgical trajectory system can aid in both theinsertion and positioning of the access instruments themselves, as wellas, aiding in the later insertion of instruments and/or implants throughthe surgical access instruments. One significant advantage is theability to later visually align surgical instruments and/or implantsalong the same trajectory by visually comparing the alignment of theinstrument to that of the access instrument The

Neurophysiologic monitoring may be carried out in conjunction with thetrajectory monitoring performed by the surgical trajectory system. Thesurgical trajectory system may be used in combination withneurophysiologic monitoring systems to conduct pedicle integrityassessments before, during, and after pilot hole formation, as well asto detect the proximity of nerves while advancing and withdrawing thesurgical instrument from the pedicle target site. By way of exampleonly, a neurophysiology system is described which may be used inconjunction with the surgical trajectory system.

The neurophysiology system includes a display, a control unit, a patientmodule, an EMG harness, including eight pairs of EMG electrodes and areturn electrode coupled to the patient module, and a host of surgicalaccessories (including an electric coupling device) capable of beingcoupled to the patient module via one or more accessory cables.

To perform the neurophysiologic monitoring, the surgical instrument isconfigured to transmit a stimulation signal from the neurophysiologysystem to the target body tissue (e.g. the pedicle). As previouslymentioned, the surgical instrument probe members may be formed ofmaterial capable of conducting the electric signal. To prevent shuntingof the stimulation signal, the probe members may be insulated, with anelectrode region near the distal end of the probe member for deliveringthe electric signal and a coupling region near the proximal end of theprobe member for coupling to the neurophysiology system.

The neurophysiology system performs nerve monitoring during surgery bymeasuring the degree of communication between a stimulation signal andnerves or nerve roots situated near the stimulation site. To do this,the surgical instrument is communicatively linked to the neurophysiologymonitoring system and stimulation signals are emitted from an electroderegion on the surgical instrument. EMG electrodes positioned over theappropriate muscles measure EMG responses corresponding to thestimulation signals. The relationship between the EMG responses and thestimulation signals are then analyzed and the results are conveyed tothe practitioner (e.g. audibly and/or visually on the neurophysiologydisplay). More specifically, the system determines a threshold currentlevel at which an evoked muscle response is generated (i.e. the loweststimulation current that elicits a predetermined muscle response).Generally the closer the electrode is to a nerve, the lower thestimulation threshold. Thus, as the probe member moves closer to anerve, the stimulation threshold will decrease, which may becommunicated to the practitioner to alert him or her to the presence ofa nerve. The pedicle integrity test, meanwhile, works on the underlyingtheory that given the insulating character of bone, a higher stimulationcurrent is required to evoke an EMG response when the stimulation signalis applied to an intact pedicle, as opposed to a breached pedicle. Thus,if EMG responses are evoked by stimulation currents lower than apredetermined safe level, the surgeon may be alerted to a possiblebreach.

In one embodiment, the tilt sensor may be communicatively linkeddirectly to the control unit of the neurophysiology monitoring systemand data from the tilt sensor may audibly communicated and/or visuallycommunicated alone and/or jointly with the neurophysiologic data.

BRIEF DESCRIPTION OF THE DRAWINGS

Many advantages of the present invention will be apparent to thoseskilled in the art with a reading of this specification in conjunctionwith the attached drawings, wherein like reference numerals are appliedto like elements and wherein:

FIG. 1 is an exemplary view of a surgical trajectory system, including atilt sensor and an LCD feedback device, connected to a surgicalinstrument, according to one embodiment of the present invention;

FIG. 2 is a perspective view of a tilt sensor of the surgical trajectorysystem of FIG. 1, according to one embodiment of the present invention;

FIG. 3 is a perspective view of a tilt sensor, the outer housing shownin dashed lines to make visible the inclinometer situated within thehousing, according to one embodiment of the present invention;

FIG. 4 is a perspective view depicting the bottom of the tilt sensor,according to one embodiment of the present invention;

FIGS. 5-7 illustrate a universal clip connector used to attach the tiltsensor of FIG. 2 to a surgical instrument, according to one embodimentof the present invention;

FIG. 8 is an exploded view of the universal clip connector of FIGS. 5-7,according to one embodiment of the present invention;

FIG. 9 is a perspective view of the tilt sensor mated with the universalclip, according to one embodiment of the present invention;

FIGS. 10A-10B illustrate a way in which the universal clip may securelycouple a surgical instrument, according to one embodiment of the presentinvention;

FIG. 11 is a perspective view of a surgical instrument (e.g. jamsheedineedle) for penetrating pedicle bone to form a pilot hole, which islinked to the surgical trajectory system of FIG. 1, according to oneembodiment of the present invention;

FIG. 12 is a perspective view of a surgical instrument (e.g. gear shiftprobe) for penetrating pedicle bone to form a pilot hole, which islinked to the surgical trajectory system of FIG. 1, according to anotherembodiment of the present invention;

FIG. 13 is a perspective view of the surgical instrument of FIG. 12coupled to the surgical trajectory system by a universal clip as opposedto the direct coupling seen in FIG. 12, according to yet anotherembodiment of the present invention;

FIG. 14 is a top view of a bubble level device optionally provided withthe tilt sensor, according to one embodiment of the present invention;

FIG. 15 is an exemplary display unit, releasably or permanently coupledto the universal clip, such that the display feedback may be viewed inthe surgical field, according to one embodiment of the presentinvention;

FIG. 16 is a front view of the display unit of FIG. 15, engaged to asurgical instrument, according to one embodiment of the presentinvention;

FIG. 17 illustrates the position of the display unit of FIG. 16 relativeto the manipulating hand of the practitioner, according to oneembodiment of the present invention;

FIGS. 18A-18B are front and side views, respectively, of the displayunit of FIG. 15 attached directly to the practitioner's manipulatinghand, according to another embodiment of the present invention;

FIG. 19 illustrates a superior view preoperative MRI image used todetermine the proper medial-lateral angle for hole formation, accordingto one embodiment of the present invention;

FIG. 20 illustrates an intraoperative lateral fluoroscopy image used todetermine the proper cranial-caudal angle for hole formation, accordingto one embodiment of the present invention;

FIG. 21 is a perspective view of a bubble needle for ensuring a truevertical reference line in fluoroscopy images, according to oneembodiment of the present invention;

FIG. 22 is a top view of a handle portion of the bubble needle of FIG.21 illustrating the level device used to orient the needle vertically;

FIG. 23 is a perspective view of a digital protractor device configuredfor use with the surgical trajectory system of FIG. 1 to determine anglemeasurements, according to one embodiment of the present invention;

FIG. 24A is a back view illustrating the protractor device of FIG. 23 ina first position aligned with a vertical reference line in theintraoperative lateral fluoroscopy image of FIG. 20, according to oneembodiment of the present invention;

FIG. 24B is a back view illustrating the protractor device of FIG. 23 ina second position aligned with the desired pedicle trajectory on theintraoperative lateral fluoroscopy image of FIG. 20, according to oneembodiment of the present invention;

FIG. 25 is a display unit for providing feedback from multiple tiltsensors, according to one embodiment of the present invention;

FIG. 26 is an illustration of an operating theater equipped with asurgical table, C-arm fluoroscope, fluoroscope monitor, practitioner,and patient;

FIG. 27 is a front view of the C-arm of FIG. 26 oriented in an A/Pposition for generating an A/P fluoroscopic image;

FIG. 28 is front view of the C-arm of FIG. 26 oriented in a lateralposition for generating a lateral fluoroscopic image;

FIGS. 29A-29B are front views of the C-arm of FIG. 26 oriented accordingto desired medial-lateral angles between the A/P position of FIG. 27 andthe lateral position of FIG. 28;

FIGS. 30A-30B are side views of the C-arm of FIG. 26 oriented accordingto various cranial-caudal angles;

FIG. 31 is a perspective view of a coupler for coupling the surgicaltrajectory system of FIG. 1 to the C-arm of FIG. 26, according to oneembodiment of the present invention;

FIG. 32 is a front view of the coupler of FIG. 31, according to oneembodiment of the present invention;

FIG. 33 is a side view of the coupler of FIG. 31 with a sensor bedaligned in a horizontal position, according to one embodiment of thepresent invention;

FIG. 34 is a side view of the coupler of FIG. 31 with a sensor bedaligned in a vertical position, according to one embodiment of thepresent invention;

FIG. 35 is a perspective view of the coupler of FIG. 31 with the tiltsensor of FIG. 2 engaged in the sensor bed, according to one embodimentof the present invention;

FIG. 36 is a side view of the coupler/tilt sensor combination of FIG. 35attached to a signal receiver of the C-arm of FIG. 26 in the A/Pposition, according to one embodiment of the present invention;

FIG. 37 is a side view of the coupler/tilt sensor combination of FIG. 35attached to a signal receiver of the C-arm of FIG. 26 in the lateralposition, according to one embodiment of the present invention;

FIG. 38 is a perspective view of a coupler for coupling the surgicaltrajectory system of FIG. 1 to the C-arm of FIG. 26, according toanother embodiment of the present invention;

FIG. 39 is a side view of the coupler of FIG. 38, according to oneembodiment of the present invention;

FIG. 40 is bottom view of the coupler of FIG. 38, according to oneembodiment of the present invention;

FIG. 41 is a front view of the coupler of FIG. 38 and tilt sensor ofFIG. 1 attached to the signal receiver face of the C-arm of FIG. 26,according to one embodiment of the present invention;

FIG. 42 is a side view of the coupler/tilt sensor combination of FIG. 41attached to a signal receiver of the C-arm of FIG. 26 in the A/Pposition, according to one embodiment of the present invention;

FIG. 43 is a side view of the coupler/tilt sensor combination of FIG. 41attached to a signal receiver of the C-arm of FIG. 26 in the lateralposition, according to one embodiment of the present invention;

FIG. 44 is a perspective view of a target containing a radio-densemarker for augmenting a radio-dense marker included with the coupler ofFIG. 38, according to one embodiment of the present invention;

FIG. 45 is a front view of the target of FIG. 44 in use with the couplerof FIG. 38, according to one embodiment of the present invention;

FIG. 46 is a front view of the coupler of a coupler for coupling thesurgical trajectory system of FIG. 1 to the C-arm of FIG. 6, the couplerincluding 4 radio-dense markers positionable over the signal receiver,according to another embodiment of the present invention;

FIG. 47 is a front view showing a surgical table rotated laterally toadjust the orientation of the C-arm of FIG. 26 with respect to thepatient, according to another embodiment of the present invention;

FIG. 48 is a side view showing a surgical table rotated in the sagittalplane to adjust the orientation of the C-arm of FIG. 26 with respect tothe patient, according to another embodiment of the present invention;

FIG. 49 is a top view of a vertebral body showing the medial-lateralangle A1 of the pedicle axis;

FIG. 50 is a side view of a vertebral body showing the cranial-caudalangle A2 of the pedicle axis;

FIG. 51 is a true A/P image of the spine with a vertical reference lineformed by the coupler of FIG. 38, according to one embodiment of thepresent invention;

FIG. 52 is a true lateral image of the spine with a vertical referenceline formed by the coupler of FIG. 38, according to one embodiment ofthe present invention;

FIG. 53 is a trajectory lateral image of the spine where the C-arm hasbeen rotated to align the vertical reference line with the pedicle axis,according to one embodiment of the present invention;

FIG. 54 is an A/P image of the spine used to determine the startingpoint for pilot hole formation through the pedicle, the A/P image beingtaken while maintaining the lateral trajectory of the C-arm as set as inFIG. 53, according to one embodiment of the present invention;

FIG. 55 is a trajectory lateral image for verifying the depth ofpenetration through a pedicle, according to one embodiment of thepresent invention;

FIG. 56 is an “owls eye view” (i.e. looking straight along the pedicleaxis) of the pedicle generated by orienting the C-arm with both themedial-lateral and cranial-caudal angles of the pedicle axis, accordingto one embodiment of the present invention;

FIG. 57 is a side view illustrating the use of a tissue distractionassembly (comprising a plurality of dilating cannulae over a K-wire) todistract tissue between the skin of the patient and the surgical targetsite, according to one embodiment of the present invention;

FIG. 58 is a perspective view of a tissue retraction assembly (in use)forming part of a surgical access system, according to one embodiment ofthe present invention;

FIG. 59 is a side view of a retractor assembly according to the presentinvention, comprising a handle assembly having three (3) retractorblades extending therefrom disposed over a dilating assembly, accordingto one embodiment of the present invention;

FIG. 60 is a side view illustrating the use of a tissue distractionassembly (comprising a plurality of dilating cannulae over a K-wire) todistract tissue between the skin of the patient and the surgical targetsite with a tilt sensor attached to the distraction assembly to monitorthe angle of insertion, according to one embodiment of the presentinvention;

FIG. 61 is a side view of a surgical trajectory system, including a tiltsensor attached via a universal clip to a post connected to a firstretractor blade, an LCD feedback device, and a tissue retractor,according to one embodiment of the present invention;

FIG. 62 is a side view of a surgical trajectory system, including a tiltsensor attached via a universal clip to a post comprising part of anarticulating arm to which the retractor is attached, an LCD feedbackdevice, and a tissue retractor, according to one embodiment of thepresent invention;

FIG. 63 is an exemplary view of a surgical trajectory system, includinga tilt sensor attached positioned directly onto the surface of thetissue retraction of FIG. 60, according to one embodiment of the presentinvention;

FIG. 64 is an exemplary view of a neurophysiology system capableconnecting the pedicle access probe in order to conduct various nervemonitoring functions; according to one embodiment of the presentinvention;

FIG. 65 is a perspective view showing the surgical instrument of FIG. 11linked to both the surgical trajectory system of FIG. 1 and theneurophysiology monitoring system of FIG. 66, according to oneembodiment of the present invention;

FIG. 66 is a perspective view showing the surgical instrument of FIG. 12linked to both the surgical trajectory system of FIG. 1 and theneurophysiology monitoring system of FIG. 66, according to oneembodiment of the present invention

FIG. 67 is an exemplary screen display of the surgical trajectory system10 incorporating both alpha-numeric and graphical indicia, according toone embodiment of the present invention; and FIG. 68 is an exemplaryscreen display of the surgical trajectory system 10 incorporating bothalpha-numeric and graphical indicia, according to another embodiment ofthe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Illustrative embodiments of the invention are described below. In theinterest of clarity, not all features of an actual implementation aredescribed in this specification. It will of course be appreciated thatin the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure. The systems disclosed herein boast a variety ofinventive features and components that warrant patent protection, bothindividually and in combination.

Various embodiments are described of a trajectory monitoring system andsurgical uses thereof for enhancing the safety and efficiency ofsurgical procedures. In one example, set forth by way of example only,the present invention may facilitate safe and reproducible pedicle screwplacement by monitoring the axial trajectory of various surgicalinstruments used during pilot hole formation and/or screw insertion. Inanother example, set forth by way of example only, intraoperativeimaging performance may be improved and radiation exposure minimized bymonitoring the precise orientation of the imaging device. In yet anotherexample, monitoring the orientation of surgical access instruments canaid in both the insertion and positioning of the access instrumentsthemselves, as well as, aiding in the later insertion of instrumentsand/or implants through the surgical access instruments. While the aboveexamples are described in more detail below, it is expressly noted thatthey are set forth by way of example and that the present invention maybe suitable for use in any number of additional surgical actions wherethe angular orientation or trajectory of instrumentation and/or implantsis important. By way of example only, the present invention may beuseful in directing, among other things, the formation of tunnels forligament or tendon repair and the placement of facet screws.Accordingly, it will be appreciated then that while the surgicaltrajectory system is generally discussed herein as being attached toinstruments such as pedicle access tools, C-arms, dilating cannulas, andtissue retractors, other instruments (e.g. drills, screw drivers, taps,inserters, etc. . . . ) may be substituted depending on the surgicalprocedure being performed and/or the needs of the surgeon. In a furtheraspect of the present invention, the trajectory monitoring system may beused in conjunction with, or integrated into, a neurophysiology systemfor assessing one or more of pedicle integrity and nerve proximity,among others functions, as will be described below.

Details of the surgical trajectory system are discussed in conjunctionwith a first exemplary use thereof for monitoring pilot hole formation(and/or screw insertion) during pedicle screw placement. As used herein,pilot hole formation is meant to encompass any of, or any combinationof, creating a hole in bone (such as, for example only, by awling,boring, drilling, etc. . . . ) and preparing a previously formed hole(such as, for example only, by tapping the hole).

With reference now to FIG. 1, there is shown, by way of example only,one embodiment of a surgical trajectory system 10 engaged with asurgical instrument 12 for accessing a pedicle. The surgical trajectorysystem 10 comprises an angle-measuring device (hereafter “tilt sensor”)14 and a feedback device 16. The tilt sensor 14 measures its own angularorientation with respect to a reference axis, such as vertical orgravity. The feedback device 16 displays the angle measurements obtainedby the tilt sensor 14 for reference by a practitioner. By attaching thetilt sensor 14 to a surgical instrument in a known positionalrelationship, the angular orientation of the instrument may bedetermined with respect to the same reference axis. This enables thesurgeon to position and maintain the instrument 12 along a desiredtrajectory path during use. For example, during pilot hole formation,surgical instrument 12 may be aligned and advanced along apre-determined pedicle axis, thereby decreasing the risk of breachingthe pedicle wall.

Tilt sensor 14, illustrated in FIGS. 2-4, includes a sensor package 17(FIG. 3) enclosed within a housing 18. The housing 18 may be made from asurgical grade plastic, metal, or any material suitable for use in thesurgical field. Housing 18 may be dimensioned to snugly mate with auniversal clip 26, described below, for attaching tilt sensor 14 tosurgical instrument 12. As shown herein, housing 18 has a generallyrectangular box shape. However, it should be understood that housing 18may be provided in any suitable shape having any suitable cross-section(e.g. generally ellipsoidal, triangular, or other polygonal shape),provided that the sensor package 17 inside the housing may be positionedsuch that it is oriented orthogonally relative to the direction ofgravity, without deviating from the scope of the invention. An alignmentgroove 20, shown by way of example only on the top of housing 18 in FIG.2, may be provided to assist in properly positioning tilt senor 14relative to the instrument 12. Specifically, groove 20 cooperates with acomplementary structure, such as alignment ridge 44 on the universalclip 26 (FIG. 6) such that the tilt sensor 14 may only attach to theclip in a single, known orientation. An engagement tab 22, shown by wayof example only on the bottom of housing 18 in FIG. 4, may be includedto assist in securing tilt sensor 14 to universal clip 26, therebypreventing movement and/or dislodgment of the tilt sensor 14. One ormore additional grooves 25 may be included on housing 18 to provideincreased grip during handling (e.g. during insertion and removal of thetilt sensor 14). In another embodiment, (not shown) the tilt sensor 14may be permanently attached to the instrument 12. In still anotherembodiment (not shown) the tilt sensor may be integrated within theinstrument.

In one embodiment, sensor package 17 comprises a 2-axis accelerometerthat measures angular orientation with respect to the acting directionof gravity. The angular orientation of tilt sensor 14 is measured in asagittal plane and a transverse plane. By way of example, theorientation of the tilt sensor 14 in the sagittal plane represents acranial-caudal angle A2(i) with respect to the direction of gravity andthe patient. Orientation in the transverse plane represents amedial-lateral angle A1(i) with respect to a patient and the directionof gravity. Sensor package 17 is preferably situated within housing 18such that when housing 18 is perpendicular to the direction of gravity,the accelerometer registers zero angle in both the sagittal andtransverse planes (i.e. the zero-angle position or A1(i)=0 and A2(i)=0).In other words, both the cranial-caudal angle and medial-lateral angleare equal to zero. Thus, when tilt sensor 14 is fixed perpendicular tothe longitudinal axis of the surgical instrument 12, the angularorientation of the instruments longitudinal axis may be determinedrelative to gravity.

Utilizing only a 2-axis accelerometer, the accuracy of the tilt sensor14 may be adversely affected by movement around the third, rotationalaxis. To counter this, measurements should preferably be taken only whenat least one of the longitudinal axis 178 and transverse axis 180 tiltsensor 14 are aligned with a selected reference frame, such as forexample, the longitudinal axis of the patient's spine (i.e. the tiltsensor 14 should be in approximately the same rotational alignment forevery measurement). In one embodiment, this may be accomplishedeffectively using visual aids to help keep the tilt sensor 14 in linewith the reference frame and/or ensure measurements may be taken onlywhen the tilt sensor 14 appears to be in this correct rotationalposition. In the event the surgical instrument 12 is inadvertently orpurposely rotated during use, the practitioner need only continue, orreverse rotation until the tilt sensor 14 again appears to beperpendicular to the long axis of the spine. Alternatively (or inaddition to), various markings or other indicia (not shown) may beincluded on one or more of the tilt sensor 14, the surgical instrument12, and the universal clip 26, to ensure proper alignment prior toobtaining measurements.

In an alternative embodiment, the sensor package 17 may be configuredsuch that it may account for, or at least measure, rotation (e.g. a“3-axis sensor”). In one embodiment, the sensor package 17 includes a2-axis accelerometer augmented by a gyroscope (not shown), which maycomprise any number of commercially available gyroscopes. While theaccelerometer again measures the angular orientation of the tilt sensor14 with respect to gravity, the gyroscope detects movement about therotational or z-axis. By monitoring the rate of rotation and time, thesystem 10 may determine the degrees of rotation imparted on the surgicalinstrument (and tilt sensor 14). The feedback device 16 may indicate tothe user that the sensor 14 is not aligned in the correct referenceframe such that the user may take steps to correct the alignment priorto taking measurements. The feedback device 16 may display feedbackaccording to any number of suitable methods. By way of example, thefeedback may utilize numeric indicia to indicate the degree ofmisalignment, color indicia, such as red or green indicating therotational status (e.g. aligned or misaligned), audible alert tones(e.g. low frequency tones for non-alignment and high frequency tones forproper alignment or visa versa or any combination thereof), etc. . . .Alternatively, the system 10 may be configured to correct the angle dataoutput based on the degree of rotation detected. In this manner, angledata from the tilt sensor may be acquired from any rotational position.A button (not shown) may be provided on the tilt sensor 14 and/orfeedback device 16 to initially zero the sensor package 17 when it isaligned with the reference frame.

In another embodiment, the sensor package 17 accounts for rotationalmovement by utilizing magnetometers (not shown) in conjunction with the2-axis accelerometers, where the magnetometer may comprise any number ofcommercially available magnetometers. The sensor package 17 includes atriplet of magnetic sensors oriented perpendicular to each other, onepointing in the x-axis, one in the y-axis, and third pointing in thez-axis. The magnetic sensors in the x and y axis act as a compass andcalculate a heading of tilt sensor 14 relative to magnetic north. Thethird magnetometer in the z-axis and the x and y axis accelerometersmonitor the tilt permitting the “compass” to work when it is not levelto the ground. Since the sensor package 17 monitors for angularorientation in the x-axis and y-axis and maintains a constant headingreference, the system 10 may calculate the amount of axial rotationrelative to an established reference frame (i.e. the patient). Thefeedback device 16 may again be configured to indicate the rotationalstatus of the tilt sensor 14 to the user, allowing them to realign thesensor 17 with the proper reference frame prior to establishing areading. The feedback device 16 may again utilize numeric indicia toindicate the degree of misalignment, color indicia, such as red or greenindicating the rotational status (e.g. aligned or misaligned), audiblealert tones (e.g. low frequency and/or volume tones for non-alignmentand high frequency and/or volume tones for proper alignment or visaversa or any combination thereof), etc.

With reference to FIGS. 5-10, there is shown one example of a universalclip 26 for mating tilt sensor 14 to the surgical instrument 12.Universal clip 26 comprises a sensor bed 28, a coupler 30, a fastener32, and a collar 34. Sensor bed 28 has an exterior surface 36, aninterior surface 38, and an opening 40. Interior surface 36 and opening40 collectively form cavity 42. Sensor bed 28 is generally rectangularin shape, however, it should be understood that sensor bed 28 may beprovided in any suitable shape having any suitable cross-section (e.g.generally ellipsoidal, triangular, or other polygonal shape) to receivethe tilt sensor 14 therein in a known orientation. Cavity 42 isdimensioned to snugly receive at least a portion of tilt sensor 14. Analignment ridge 44 may be provided along an upper region of interiorsurface 38 of cavity 42, shown by way of example only along the top, toensure tilt sensor 14 is positioned properly within the cavity 42 (e.g.with the top surface of housing 18 adjacent to the upper region of theinterior surface 38). Alignment ridge 44 is complementary to alignmentgroove 20 on the tilt sensor housing 18. In order to insert the tiltsensor 14 in cavity 42, the alignment ridge 44 and alignment groove 20must be aligned. Thus, tilt sensor 14 may preferably only fit togetherwith the sensor bed 28 in a single, known orientation. To secure thetilt sensor 14, a hole 45 is provided within a lower region of theinterior surface 38 (FIG. 7), which receives a complementary protrusion24 situated on engagement tab 22 of sensor housing 18. When the tiltsensor 14 is fully inserted into cavity 42, protrusion 24 becomes seatedin hole 45, thereby preventing the unintentional disengagement of tiltsensor 14 from the sensor bed 28. It should be understood that variousother retaining mechanisms (not shown) may be used in place of, or inaddition to, the protrusion/hole engagement described above. Otherretaining mechanisms may include, but are not necessarily limited to, aball-spring mechanism and a clasp.

Sensor bed 28 is attached to coupler 30. For stability, sensor bed 28and coupler 30 may preferably be formed of a single member. Coupler 30comprises a generally tubular member including a first hollow portion 46and a second hollow portion 47. First hollow portion 46 attaches tosensor bed 28 and retains a receptacle 50. Second hollow portion 48retains an engagement end 52 of fastener 32. The receptacle 50 andengagement end 52 may be communicatively linked within coupler 30. Thesecond portion 48 preferably has external threading 49 that iscomplementary to internal threading 53 on collar 34, allowing the collar34 to move laterally along the second portion by twisting the collar 34.The free end 54 of fastener 32 is configured to tightly grasp instrument12. By way of example only, the free end may comprise a hook. Ifneurophysiology monitoring is to be used, as described below, receptacle50 can be employed to couple the universal clip 26 to a neurophysiologymonitoring system. Because the receptacle 50 and fastener 32 arecommunicatively linked within coupler 30, stimulation signals may bepassed from the neurophysiology monitoring system to the instrument 12.

With reference to FIGS. 10A-10B, to secure a surgical instrument 12 touniversal clip 26, a portion of surgical instrument 12 (shown incross-section) is positioned within the hook of free end 54 (FIG. 10A).Collar 34 may then be twisted in a first direction to laterallydisplaced collar 34 toward the free end 54 so as to capture surgicalinstrument 12 between the collar 34 and free end 54 (FIG. 10B). Whenfully tightened, universal clip 26 is securely fastened to instrument 12and extends perpendicular to the longitudinal axis of surgicalinstrument 12. When tilt sensor 14 is engaged with clip 26, tilt sensor14 also extends perpendicular to the longitudinal axis of instrument 12.To release the surgical instrument 12, collar 34 may be twisted in theopposite direction (FIG. 10A).

A surgical instrument 12, according to one embodiment, is illustrated inFIG. 11. Surgical instrument 12 may comprise a pedicle access probe. Byway of example only, instrument 12 may be any of the insulated pedicleaccess probes described in detail in the commonly owned and co-pendingU.S. patent application Ser. No. 11/448,237, entitled “Insulated PedicleAccess System and Related Methods,” and filed on Jun. 6, 2006, theentire contents of which is incorporated by reference as if set forthherein in its entirety. Instrument 12 comprises generally a probe member60, having a longitudinal axis 61, and a handle 62. Probe member 60 maybe embodied in any variety of configurations that can be insertedthrough an operating corridor to a pedicle target site and bore, pierce,or otherwise dislodge and/or impact bone to form a pilot hole forpedicle screw placement. Probe member 60 may be generally cylindrical inshape, however, probe member 60 may be provided in any suitable shapehaving any suitable cross-section (e.g. generally oval, polygonal, etc.. . . ). A distal region 64 of probe member 60 may have a shaped tip 66formed of any number of shapes generally suited to effect pilot holeformation, such as, by way of example only, a beveled point, doublediamond, drill bit, tap, and a generally tapered awl. A proximal region68 of probe member 60 may be configured to couple with universal clip26. Probe member 60 may be composed of any material suitable forsurgical use and strong enough to impact bone to form a pilot hole. Inone embodiment, the material may also be capable of conducting anelectric current signal to allow for the use of neurophysiologicmonitoring. By way of example only, probe member 60 may be composed oftitanium, stainless steel, or other surgical grade alloy.

Handle 62 may be permanently or removably attached to probe member 60along the proximal region 68. Handle 62 may be shaped and dimensioned inany of a number of suitable variations to assist in manipulating probemember 60. By way of example only, the handle 62 may be generallyT-shaped such as the handle pictured in FIG. 11. Other suitable shapesfor handle 62 may include, but are not necessarily limited to, generallyspherical, ellipsoidal, and egg-shaped. Universal clip 26 may preferablygrasp the proximal end 68 of probe member 60 through a cutout in thehandle 62. If the handle does not have a cutout the universal clip 26may attach to the probe member 60 below the handle 62. Universal clip 26forms a sturdy connection with probe member 60 such that the tilt sensor14 is maintained in a position perpendicular to the longitudinal axis 61of probe member 60. When the longitudinal axis 61 of probe member 60 isparallel to the direction of gravity, the tilt sensor 14 isperpendicular to the direction of gravity (i.e. the zero-angleposition). In other words, when the longitudinal axis 61 of probe member60 is parallel to the acting direction of gravity, both thecranial-caudal angle and the medial-lateral angle will be zero-degrees.

With reference to FIG. 12, there is shown another example of a pedicleaccess instrument that may be used with the surgical trajectory system10. Surgical instrument 80 is similar to a standard gearshift probe,which are commonly used to create holes in pedicle bone, modified fordirect engagement with the tilt sensor 14. Surgical instrument 80comprises a probe member 82, a handle 84, an orientation shaft 86, and asensor cavity 88 for receiving and holding a tilt sensor 14. Probemember 82 may be generally cylindrical in shape and include a distal end90, a proximal end 92, and a longitudinal axis 94 extending throughdistal and proximal ends 90, 92, respectively. However, it should beunderstood that probe member 82 may be provided in any suitable shapehaving any suitable cross-section (e.g. generally oval, polygonal, etc.. . . ). The distal end 90 may have a shaped end comprising any of anumber of forms generally suited to effect pilot hole formation such as(by way of example only) a beveled point, drill bit, or as shown in FIG.12, an awl with a generally tapered shape. Probe member 82 may becomposed of, by way of example only, titanium, stainless steel, or othermaterial strong enough to impact bone to form a pilot. In one embodimentthe material of probe member 82 is capable of conducting an electricsignal for employing neurophysiologic monitoring, as described below.Probe member 82 may include one or more markings 96 about the exteriorsurface that can be viewed to indicate the depth of penetration in apedicle target site.

Handle 84 may be permanently or removably attached to probe member 82 atthe proximal end 92. Handle 84 may be shaped and dimensioned in any of anumber of suitable variations to assist in manipulating probe member 82.By way of example only, the handle 84 may be generally spherical shaped,T-shaped, or egg shaped, to name a few. With further reference to FIG.12, an orientation shaft 86 may be positioned on handle 84. Orientationshaft 86 extends from handle 84 perpendicularly to the longitudinal axis94 of the probe member 82. The handle 84 also includes a sensor cavity88. The sensor cavity 88 functions to receive and hold the tilt sensor14 in proper position relative to the probe member 82. The sensor cavity88 may preferably be dimensioned to snugly receive at least a portion ofthe tilt sensor 14, thereby preventing movement of the tilt sensor 28within the cavity 88. One or more mechanisms may be provided on the tiltsensor 14 and/or on or within the sensor cavity 88 to secure the tiltsensor 14 in position. Preferably, sensor cavity 88 may include a holeor recess (not shown) for capturing the protrusion 24 on tilt sensor 14,described above. Other such mechanisms may include, but are notnecessarily limited to, a ball-spring mechanism and a clasp mechanism

Orientation shaft 86 may be provided as a visual marker to assist inaligning the tilt sensor 14 and surgical instrument 80 with the properreference frame (as described above) when obtaining angle measurements.Similar to that described above with reference to the universal clip 26,the orientation shaft 86 may be aligned, by way of example only,perpendicular to the longitudinal axis of the spine when a measurementis read. Again this eliminates the risk of inaccurate angle measurementsdue to rotational movement of the surgical instrument when a 2-axisaccelerometer is utilized.

In an alternate embodiment, the surgical instrument 80 may be providedwithout sensor cavity 88. Instead, the universal clip 26 may attach toprobe member 82, as illustrated in FIG. 13. In another alternateembodiment, (not shown) the tilt sensor 14 may be permanently attachedto the handle 80. In still another embodiment (not shown) the tiltsensor may be integrated within the instrument 80.

With reference to FIG. 14, a bubble level device 110 may be used toensure the tilt sensor 14 is functioning correctly. The bubble leveldevice 110 includes a handle 112 with a level 114 mounted in it. Thetilt sensor 14 is inserted into the handle 112, which then is placed ona flat surface so that an indicator ring 116 on the domed transparentsurface 117 of level 114 encircles the bubble 118 captured within thedomed surface 117. When the bubble 118 is within the indicator ring 116,the tilt sensor display should read approximately zero-degrees for boththe cranial-caudal readout 99 and medial-lateral readout 98.

Regardless of the manner of coupling the tilt sensor 14 to therespective instrument (e.g. probe 12, gear shift 80, or any otherinstrument), the feedback device 16 is communicatively linked to tiltsensor 14 to provide feedback to the surgeon regarding angle of the tiltsensor 14 and instrument relative to the desired angles (medial-lateraland cranial-caudal). This communication link may be accomplished viahard-wire (e.g. data cable 70 of FIG. 1) and/or via wireless technology,in which case the tilt sensor 14 and feedback device 16 may includeadditional hardware commonly used for enabling such wirelesscommunication. The feedback device 16 may be a computer or similar typeprocessing unit (not shown). User input may be directed to thetrajectory system 10 through feedback device 16. In one embodiment,shown in FIG. 15, feedback device 16 includes an LCD display with atleast one numerical readout 98 for presenting the medial-lateral angledetermined by the tilt sensor 14 and at least one numerical readout 99for presenting the cranial-caudal angle determined by the tilt sensor.Readouts 98 and 99 may be displayed in a single window or on separatewindows designated for each readout. In one embodiment, themedial-lateral and cranial-caudal readouts 98, 99 are displayedsimultaneously and continuously while the tilt sensor 14 is in use. Ifonly one window is provided, a switch or button for toggling between thetwo angle measurements may be utilized (not shown). The feedback device16 may be placed next to the patient on the surgical table, or it may beaffixed to any number of suitable objects in the operating room,including, but not necessarily limited to, an IV pole, surgical table,prep table, fluoroscope, neurophysiologic monitoring system, etc. . . .If communicatively linked to the feedback device 16 via hard-wire, theposition of the feedback device 16 should be such that the tilt sensor14 may move freely without tensioning the data cable 70.

At times it may not be convenient for the surgeon to look away from thesurgical field to view the angle measurements displayed by the surgicaltrajectory system 10. According to one embodiment, shown in FIGS. 15-16,this may be accomplished by providing the feedback device 16 having asmaller, thinner and/or miniaturized size relative to that shown inFIG. 1. By providing the feedback device in the manner shown in FIGS.15-16, the practitioner may be able position the feedback device 16close to his or her hand so as have the displays 98, 99 both in theirgeneral field of view while using the surgical trajectory system 10. Forexample, with reference to FIG. 17, the feedback device 16 may becoupled to the instrument 12 via a universal clip 26 such that it restsabove and slightly offset from the practitioner's hand, thus maintainingthe feedback device 16 in the surgical field without obstructing thesurgeon's view of the operative site. By way of another example, withreference to FIGS. 18A-18B, feedback device 16 may be positioned on theback of the hand of the practitioner, which may be augmented via a strap102. Again, this advantageously positions the feedback device 16 in thesurgical field without obstructing the surgeon's view of the operativesite.

It is further contemplated that feedback device 16 may be configured toprovide feedback based on indicia other than numerical readouts 98, 99.By way of example, feedback device 16 may utilize a code based on theexpression of color to indicate the angular orientation of the tiltsensor 14 and also thus, the orientation of the instrument to which itis attached. One such color code scheme will display the color red whenthe angles of the tilt sensor 14 fall outside an acceptable range fromthe correct orientation, the color yellow when the angles of the sensor14 are close to the correct range but not yet within an optimalorientation range, and the color green when the angles of the tiltsensor 14 are aligned within an optimal orientation range. The correctorientation of the tilt sensor 14 (i.e. whether it is in the “greenzone”, “yellow zone”, or “red zone”) may be measured againstpredetermined angle measurements previously inputted into the system 10or, against a separate reference marker which is known to be positionedin the correct orientation and is communicatively linked to thetrajectory system 10 (e.g. a C-arm as will be described below). A singlecolor display could be used to indicate the overall orientation of thetilt sensor 14, or, individual and independently operated color displaycould be used to indicate the orientation in the cranial-caudaldirection and medial-lateral directions, respectively. Variousimplementation methods may be utilized to accomplish the display of thecolor code. By way of example only, the LCD displays could be configuredto output a color and change the color according to the code based oninput data from the sensor 14. Alternatively, dedicated color displayscomprising one of each color in the code may be arranged such that asingle color is displayed based upon the input from the sensor 14. Twodisplays for each color may be utilized in order to show the orientationstatus of both the cranial-caudal and medial-lateral anglesindependently. LED lights may be used instead of LCD displays andarranged according to any of the above configurations. Feedback based oncolor indicia may be used alone or in combination with the numericaldata previously described.

By way of another example, the feedback device 16 may utilize a codebased on the emission of audio tones to indicate the angular orientationof the tilt sensor 14 relative to predetermined reference anglescorresponding to the pedicle axis. One method for implementing an audiocode involves varying one or more of the volume, pitch, frequency, pulserate, and length of the audio tone based on the determined orientationof the sensor 14 relative to the predetermined orientation ranges. Audiofeedback may be used alone, or in combination with one or both of thenumerical data and color indicia previously described. In oneembodiment, a first audible signal may be indicative of an optimalvariance between the trajectory of the instrument and at least one ofthe first and second determined angular relationships between the sensor14 and said reference direction. A second audible signal may beindicative of an unacceptable variance between the trajectory of theinstrument and at least one of the first and second determined angularrelationships between the sensor 14 and the reference direction. A thirdaudible signal may be indicative of an acceptable yet not optimalvariance between the trajectory of the instrument and at least one ofthe first and second determined angular relationships between the sensor14 and the reference direction.

FIG. 67-68 illustrate, by way of an example only, embodiments of ascreen display 500 capable of receiving input from a user in addition tocommunicating feedback to the user. The screen display 500 incorporatesboth alpha-numeric and color indicia as described above. In this example(though it is not a necessity) a graphical user interface is utilized toenter data directly from the screen display. By way of example,measurements obtained for the medial-lateral angle A1 may be enteredinto input boxes 504 and 506 for (for left and right pedicles,respectively). The data may be entered for each spinal level of interestby selecting the appropriate level from a menu 506 and then entering thecorrect values into boxes 504 and 506. The entered values may be savedby the system such that during the procedure selecting the spinal levelfrom menu 510 automatically recalls the inputted values. A box 508 isprovided for inputting the cranial-caudle angle A2 determined for eachlevel. A C-arm window 512 contains data pertaining to a second tiltsensor 14 positioned on a fluoroscopic imager, as is described in moredetail below. By way of example numeral boxes 514 and 516 display thenumeric values determined by the C-arm tilt sensor 14. When the numericvalues corresponding to the C-arm sensor matches within an acceptedrange the predetermined target angles the C-arm window 512, or a portionthere of (such as the circle 518) may be saturated with the color green.Alphanumeric characters may also visually indicate that the targetangles have been matched by the C-arm. If the c-arm is aligned with thepedicle axis (placed in the owls' eye view) as is later described, theC-arm values A1(c) and A2(c) should approximate the pedicle axis anglesA1 and A2. The user may have the option to base feedback from theinstrument 12, 80 mounted tilt sensor 14 (e.g. red, yellow, greenindicia, etc. . . . ) on matching the C-arm sensor values, rather thanthe predetermined target values. This option may be exercised, by way ofexample only, by selecting the appropriate button in the C-arm window512. A status bar 520 may be provided to indicate the relative status ofboth the instrument 12, 80 and C-arm tilt sensors. By way of exampleonly, the status bar 520 depicted in FIGS. 67 and 68 indicate that boththe instrument 12, 80 and the C-arm sensors are attempting to match thetargeted angles. Other messages (not shown) may indicate for example,that the instrument 12, 80 is trying to target the C-arm angles, thatthe target angles are matched, or that a sensor is not in use. FIGS.67-68 depict varying embodiments of an instrument window.

The instrument window embodied in FIG. 67, employs a color coded target.The outer rings 524 of the target may be red. The middle rings 526 ofthe target may be yellow, and the inner circle 528 may be green. Whenthe instrument is aligned with the target angles center circle may besaturated green, indicating that both the medial-lateral angle A1 andcranial-caudal angles have been matched, or A1=A1(i) and A2=A2(i).Similarly if the instrument 12, 80 is matched to the C-arm (A1(c)=A1(i)and A2(c)=A2(i)) the center circle may be saturated green. The middle526 and outer 524 rings may be divided into quadrants 530, 532, 534, and536 corresponding to right, left, cranial, and caudal, respectively. Byway of example, if the instrument is aligned to far left of the target,the outer 524 or middle 526 ring in the left quadrant 530 will besaturated depending upon how misaligned the instrument is (i.e. whetherit falls into the yellow or red range). Similarly, if the instrument 12,80 is aligned to far cranially, the outer 524 or middle 526 ring in theupper quadrant 534 will be saturated depending upon how misaligned theinstrument is. If the instrument 12, 80 has matched one of the targetedangles but not the other, only the quadrant corresponding to themisaligned angle will be saturated. The instrument window embodied inFIG. 68, employs a color coded display approximating the look of abubble level. A free floating ring 538 moves relative to the movement ofthe instrument. The closer the bubble is to the center, the closer theinstrument is to matching the target angle (or C-arm angle). When theinstrument is within the range indicating proper alignment the ring 538may be saturated green.

In general, to orient and maintain the surgical instrument 12, 80 alonga desired trajectory during pilot hole formation, the distal end ofsurgical instrument 12, 80 may first be placed on the pedicle targetsite in the zero-angle position. The universal clip 26 or orientationshaft 86 should be set in the desired reference position, preferablyperpendicular to the longitudinal axis of the spine. The surgicalinstrument 12, 80 may then be angulated in the sagittal plane until thedesired cranial-caudal angle is reached. Maintaining the propercranial-caudal angle, the surgical instrument 12, 80 may then beangulated in the transverse plane until the proper medial-lateral angleis attained. Once the feedback device 16 shows that both angles arecorrect, the instrument 12, 80 may be advanced into the pedicle to formthe pilot hole. The instrument 12, 80 may be rotated back and forth toassist in the formation of the pilot hole. To keep the proper trajectorythroughout formation, the instrument 12, 80 may occasionally berealigned so that the universal clip 26 or orientation shaft 86 is againperpendicular to the long axis of the spine and the angle measurementsrechecked. This may be repeated until the pilot hole is complete.

To form a pilot hole in a vertebral pedicle with the aid of the surgicaltrajectory system 10, the surgical instrument 12, 80 is advanced to thepedicle target site where the pilot hole is to be formed. This may bedone through any of open, mini-open, or percutaneous access. The precisestarting point for pilot hole formation may be chosen by thepractitioner based upon their individual skill, preferences, andexperience. One method which may be employed to select the startingpoint is described further below, in conjunction with methods forutilizing the tilt sensor 14 to orient a fluoroscope. In brief, a C-arm(used for fluoroscopic imaging) may be equipped with the tilt sensor 14.The C-arm may then be oriented so that the fluoroscope's x-ray beam isparallel to the axis of the pedicle in one or both axes. A pediclecross-section may be seen in the resulting images and a starting pointmay be selected.

Upon safely reaching the pedicle target site, the surgical instrument12, 80 is manipulated into the desired angular trajectory. FIGS. 19-20illustrate one exemplary method for determining the desired trajectoryangles, wherein a series of measurements are used to determine thepedicle axis of the pedicle (or more likely, pedicles) which willreceive a pedicle screw. As shown in FIG. 19, preoperative superior viewMRI or CAT scan images are obtained and used to determine themedial-lateral angle A1. A vertical reference line is drawn through thecenter of the vertebral body (in the A-P plane). A medial-lateraltrajectory line is then drawn from a central position in the pedicle(e.g. a position within the soft cancellous bone, as opposed to theharder cortical bone forming the outer perimeter of the pedicle) to ananterior point of the vertebral body for the target pedicle. Theresulting angle between the medial-lateral trajectory line and thereference line is measured and the result correlates to themedial-lateral angle A1 of the pedicle axis of the target pedicle, andthus also the medial-lateral angle to be used in forming the pilot hole.The measurement is repeated for each pedicle and the results may benoted and brought to the operating room for reference during thesurgery. As previously mentioned, in some embodiments the feedbackdevice 16 includes and/or is communicatively linked to a processorhaving memory such that the predetermined measurements may be input intothe system prior to surgery for easy retrieval and application later.

As shown in FIG. 20, the cranial-caudal angle A2 may be determined usingan intraoperative lateral fluoroscopy image. A vertical reference lineis preferably captured in the lateral fluoroscopy image to ensuremeasurements are performed with respect to the direction of gravity.Fluoroscopy image outputs can generally be rotated 360° such that theimage can appear on the monitor in any orientation and a verticalreference line prevents measurements from inadvertently being calculatedfrom an incorrect reference position. One method for generating anaccurate vertical reference line includes inserting a straight K-wire orneedle into the spinous process at the desired vertebral level. TheK-wire or needle may be oriented parallel to the acting direction ofgravity, using the tilt sensor 14 and/or a bubble needle 140. of thetype shown, by way of example, in FIGS. 21-22

The bubble needle 140 demonstrated in FIGS. 21-22 comprises a needle orprobe portion 142 and a handle 144. The needle portion 142 is composesof a biocompatible radio-dense material such that it will show up influoroscopic images. The handle 144 may be removably or permanentlyattached to the needle portion 142. Like the handle of bubble leveldevice 110, the handle of bubble needle 140 is outfitted with a level146 mounted in it. The level 146 comprises a volume of fluid (e.g.water, oil, saline, etc. . . . ) contained within at least partiallytranslucent enclosure 148 with a gas bubble 150 (e.g. oxygen, air, CO₂,etc. . . . ) disposed within the domed closure 148. The bubble 150, whenthe instrument is positioned vertically, will move to the approximatecenter of the domed enclosure 148. In this fashion, the bubble needle140 may be employed to generate a true vertical reference line duringimaging by first positioning the needle portion 142 on a desired targetsite within the site to be imaged, such as, for example only, docked onthe spinous process and then using the level 146 to align the needle 142vertically by holding the handle 144 with the bubble 150 at the centerof the domed enclosure 148. In one optional embodiment, the domedenclosure 148 may include one or more concentric circles 152 forming a“bulls-eye” on the domed enclosure 148 to aid in the positioning of thegas bubble 150 within the domed enclosure 148. Although described hereinas a “gas bubble” it will be appreciated that this “targeting” substancemay be another liquid having a lighter molecular weight than the basefluid.

As an alternative, the vertical reference line may be generated bypositioning a radio dense marker on the C-arm rather than the patient.Exemplary embodiments of such radio dense markers and methods forpositioning them on the C-arm are described below in more detail. Thelateral fluoroscopy image of FIG. 20 is shown with the verticalreference line visible in the center of the image. A cranial-caudaltrajectory line is drawn from the pedicle nucleus to an anterior pointof the vertebral body for the target pedicle. The resulting anglecalculated between the cranial-caudal trajectory line and the verticalreference line is the cranial-caudal angle A2 of the pedicle axis and isthe angle measurement to be used in forming the pilot hole. These stepsshould be repeated for each pedicle that is to receive a pedicle screw.It will be appreciated that while the cranial-caudal angle A2 isgenerally described herein as being determine intraoperatively, it isalso contemplated that angle A2 may be determined preoperatively as wellby combining various medical imaging and computer processing techniquesto recreate the vertebra of interest and allowing the pedicle axis, tobe calculated prior to surgery.

According to one embodiment, shown in FIGS. 23-24, a protractor 120 maybe provided with system 10 to assist in determining the cranial-caudalangle from the intraoperative image. The protractor 120 includes ahandle 122 and a blade 124. A proximal end 126 of handle 122 comprises asensor bed 128. Sensor bed 128 is similar to sensor bed 28 describedabove with reference to universal clip 26, and preferably engages tiltsensor 14 in the same manner. In other embodiments (not shown) the tiltsensor 14 may be permanently attached to or integrated within the handle122 Blade 124 is generally flat and rectangular in shape with generallyflat and triangular buttress element 125 extending generallyperpendicularly from the top and distal region of the blade 124. Thedistal edge of the blade 124 is coplanar with the distal edge of thebuttress element 125 such that each may be disposed against a flatsurface (e.g. fluoroscope monitor) at the same time. The blade 124attaches at its proximal end to a distal end 130 of handle 122. Aftertaking the intraoperative lateral fluoroscopy image, the protractor 120is used at the C-arm screen to measure the desired cranial-caudal angle.The blade 124 is lined up with the vertical reference line (FIG. 24A).Because the fluoroscopy image may not be aligned properly on thefluoroscope imaging monitor, the tilt sensor 14 may be set to zero whenit is lined up with the vertical reference line. A button (not shown)may be provided on one of the tilt sensor 14 and feedback device 16 toselectively zero out of the sensor 14. The protractor 120 is thenrotated about its longitudinal axis until the blade 124 lines up withthe pedicle trajectory line (FIG. 24B). Feedback device 16 will displaythe numerical readout 99 for the angle between the vertical referenceline and the pedicle trajectory line (i.e. the cranial-caudal angle) asmeasured by the tilt sensor 14.

With reference to FIG. 25, there is shown an alternate embodiment of afeedback device 134 which is configured to communicatively link multipletilt sensors 14 at once. Feedback device 134 may be linked to three tiltsensors 14 individually or simultaneously and angle measurements may beprovided individually or simultaneously for all attached tilt sensors14. In one example, this allows a tilt sensor 14 to be engaged with aninstrument such as pedicle access probe 12, the protractor 120, and (notshown) a C-arm without the need for multiple displays and/or connectingand disconnecting the tilt sensor 14 to the various devices during theprocedure.

Once the desired trajectory angles are determined for the necessarypedicles, pilot holes may be formed and screws inserted using the tiltsensor 14 to ensure the instruments and implants are aligned with thedetermined angles. As mentioned above, the safety and reproducibility ofpilot hole formation may be further enhanced by employingneurophysiologic monitoring, as will be described in detail below, inconjunction with the trajectory monitoring performed by the surgicaltrajectory system 10.

The surgical trajectory system 10 of the present invention may provideadditional advantages during surgery when used to enhance intraoperativeimaging commonly performed during many surgical procedures. C-armfluoroscopes are used extensively during many surgical procedures.During spinal surgery for example, the C-arm is used frequently to helplocate specific structures of the spine, to direct the positioning ofsurgical instruments and/or instrumentation, and to verify the properalignment and height of vertebra, among other uses. As will be clearfrom the description herein, augmenting C-arm usage with the surgicaltrajectory system 10 may increase efficiency and reduce radiationexposure associate with using the C-arm by eliminating much of the guesswork and trial and error that is often required to achieve the desiredfluoroscopic image.

With reference to FIG. 26, there is shown a typical operating theatre200 in which a practitioner 202 may perform surgical procedures on apatient 204. The patient 204 is positioned on a radio-opaque operatingtable 206. Arrayed around the table 206 are a standard C-arm 208,comprising a frame 210, a signal transmitter 212, and a signalreceiver/image intensifier 214, and a flour-monitor 216. In use, anx-ray beam 218, having a central axis 220, may be directed from thesignal transmitter 212 through a desired area of patient 204 and pickedup by the signal receiver 214. An image of the patient's 204 body tissuelocated in the path of beam 218 is generated and displayed onfluoroscope imaging monitor 216. It should be appreciated that while theC-arm 208 is discussed herein generally for use during spine surgery tocapture images of the spine, such discussion is for exemplary purposesonly. It will be understood that the C-arm 208 may be utilized forimaging in a wide variety of surgical procedures. The devices andmethods for orienting the C-arm described herein may apply equally wellto those other such procedures, and as such, fall within the scope ofthe present invention.

As illustrated in FIGS. 27-30, the C-arm frame 210 may be adjusted toalter the path of the beam 218, and thus the image that is generated. InFIG. 27 the frame 210 is oriented such that beam 220 travels parallel tothe direction of gravity. With the patient in the prone position, asshown herein, this position of frame 210 generates an anterior-posterior(A/P) image. This position of C-arm 208 is referred to hereafter as theA/P position. Rotating the frame 90° in a medial-lateral direction(through a transverse plane), as depicted in FIG. 28, directs the beam220 perpendicular to the direction of gravity and generates a lateralimage. This position of the C-arm 208 is referred to as the lateralposition. A/P and lateral images may both be useful during a spinalprocedure and the C-arm may be adjusted between the A/P and lateralpositions numerous times during the procedure. As illustrated in FIGS.29A-29B, the frame 210 may also be oriented in any position within thetransverse plane between the A/P and lateral positions, such that thebeam 220 forms an angle A1(c) (the medial-lateral angle) between zeroand 90° with respect the direction of gravity. Furthermore, asillustrated in FIGS. 30A-30B, the frame 210 may also be rotated in acranial-caudal direction (within a sagittal plane) such that the beam220 forms another angle A2(c) (the cranial-caudal angle) with respect tothe direction of gravity. By way of example only, the C-arm may beoriented such that one or both of angles A1(c) and A2(c) correspond tothe desired axis of trajectory of a pedicle bone, i.e. angles A1 and A2,as will be discussed in more detail below.

By attaching the tilt sensor 14 to the C-arm 208 in a known positionalrelationship, the angular orientation of the C-arm with respect to thereference axis (gravity) may be determined. This enables thepractitioner to quickly position the C-arm 208 in a known orientation,such as, by way of example only, the precise orientation in which aprevious image was acquired. Doing so may eliminate the time and extraradiation exposure which is often endured while acquiring numerousimages while “hunting” for the right image. Attaching the tilt sensor 14to the C-arm may further enable the practitioner to determine theangular orientation of anatomical structures within the patient (e.g.vertebral pedicles), as will be described below. This may beadvantageous, for example only, when the practitioner is performingpedicle fixation and preoperative images (such as the MRI or CAT imageswhich may be used to determine the pedicle axis angle A1) are notavailable for preoperative planning, as described above.

FIGS. 31-34 depict a coupler 222 for attaching the tilt sensor 14 to astandard C-arm 208 according to one embodiment of the invention. Coupler222 comprises a sensor bed 224 configured to receive tilt sensor 14, anda mount 226 configured to attach to the C-arm 208. Mount 226 includes abase region 228 equipped with a slot 232 spanning the distance betweenthe sides 234. In use, a strap or belt 236 (FIG. 36) may be passedthrough slot 232 and fastened around C-arm 208 to secure the coupler222, and thus the tilt sensor 14, to the C-arm 208. An upper region 238of coupler 222 contains a cutout 242 in which sensor bed 224 ispivotally attached to coupler 222 via a pin 244. Sensor bed 224 maypreferably pivot between a horizontal position (with respect to baseregion 228), illustrated in FIG. 33, and a vertical position (withrespect to base region 228), illustrated in FIG. 34. As will bedescribed below, pivoting the sensor bed 224 between the verticalposition and the horizontal position allows the tilt sensor 14 to bealigned in the same starting orientation (with respect the direction ofgravity) whether the C-arm is in the A/P position or the lateralposition. Ball-springs 240, or any of a number of other suitablemechanisms, may be positioned within cutout 242 to prevent unintentionalmovement of sensor bed 224 and maintain it in either of the desiredhorizontal or vertical positions.

Sensor bed 224 is similar to sensor bed 28 of the universal clip 26 asboth are designed to receive and secure tilt sensor 14. Bed 224 has anexterior surface 246, an interior surface 248, and an opening 250.Together, interior surface 248 and opening 250 form cavity 252. Sensorbed 224 is generally rectangular in shape, however, it should beunderstood that sensor bed 224 may be provided in any suitable shapehaving any suitable cross-section (e.g. generally ellipsoidal,triangular, or other polygonal shape) without deviating from the scopeof the invention. Cavity 252 is dimensioned to snugly receive at least aportion of tilt sensor 14. An alignment ridge 254, configured to engagetilt sensor 14 as described below, may be provided along the interiorsurface 248 (shown by way of example only along the top of sensor 14) toensure tilt sensor 14 is positioned properly (e.g. right side up) withinthe cavity 252. Additional engagement features, such as for example, ahole or indentation (not shown) may be provided to cooperate withprotrusion 24 on tab 22 help secure the tilt sensor 14 within cavity252.

To attach tilt sensor 14 to the coupler 222, the practitioner 202 orother user may grasp tilt sensor 14 and align the groove 20 of housing18 with the alignment ridge 254 of cavity 252. The tilt sensor 14 maythen be slid into the cavity until the protrusion 24 engages the hole orindentation in cavity 252. In other embodiments (not shown) the tiltsensor 14 may be permanently attached to or integrated within coupler222. FIG. 35 illustrates the tilt sensor 14 fully engaged within thesensor bed 224 of the coupler 222 and in the horizontal positionreferenced with regard to FIG. 33. Thereafter, sensor bed 224 and tiltsensor 14 may be pivoted into one or the other of the horizontal andvertical positions as needed during the procedure. FIG. 36 shows thecoupler 222 attached to the C-arm 208 oriented in the A/P position,while FIG. 37 shows the coupler 222 attached to the C-arm 208 orientedin the lateral position. In either case, the belt 236 is fastened aroundsignal receiver 214 and the base region 228 of coupler 222 rests squareand secure against a sidewall 256 of receiver 214. The bottom surface230 of mount 226 may be contoured or shaped to match the contour of theside wall 256. For example, the bottom surface 230 may have a generallyupside down “V” shape (best viewed in FIG. 32) to securely rest againstthe rounded surface of side wall 256. To orient the tilt sensor 14 inthe zero-angle position with the C-arm 208 oriented in the A/P positionof FIG. 36, the sensor bed 224 is positioned in the “vertical” positionrelative to the coupler 222 as shown in FIG. 34. To orient the tiltsensor 14 in the zero-angle position with the C-arm 208 in the lateralposition of FIG. 37, the sensor bed 224 is arranged in the “horizontal”position relative to the coupler 222 as shown in FIGS. 33 and 35. Ineither case, this positions the tilt sensor 14 perpendicular to gravity.

FIGS. 38-40 depict a coupler 260 for attaching tilt sensor 14 to astandard C-arm 208 according to another example embodiment of the presetinvention. Coupler 260 includes sensor bed 224 and a mount 262 having abase region 264 for attaching to the C-arm 208 and an upper region 266for pivotally attaching sensor bed 224 to the mount 262. In otherembodiments (not shown) the tilt sensor 14 may be permanently attachedto or integrated within coupler 260. Sensor bed 224 is pivotallyattached, via a pin 268, within a cutout 270 in upper region 266. Sensorbed 224 may preferably pivot between a horizontal position (with respectto base region 264) and a vertical position (with respect to base region264) as described above with reference to coupler 222 in FIGS. 33-35.Ball-springs 272, or any other suitable mechanism, may be positionedwithin cutout 270 to prevent unintentional movement of sensor bed 224and maintain it in either of the desired horizontal and verticalpositions.

Whereas mount 226 of coupler 222 was configured to preferably attach tothe sidewall 256 of signal receiver 214, mount 262 is configured topreferably mount to the face 258 of signal receiver 214, as illustratedin FIGS. 41-43. In one embodiment, Velcro® may be used to releasably fixmount 262 to face 258. Other attachment means, including, but notnecessarily limited to, adhesive gel and adhesive tape may be usedinstead of Velcro®. As illustrated in FIGS. 42-43, since the orientationof coupler 260 varies from that of coupler 222 by 90° when fixed to theC-arm (because coupler 222 attaches to the sidewall 256 and coupler 260attaches to the face 258), the roles of the horizontal and verticalpositions of the sensor bed 224 are reversed. When C-arm 208 is in theA/P position as in FIG. 42, the sensor bed 224 is pivoted to thehorizontal position such that the length and width of the tilt sensor 14are perpendicular to the direction of gravity. Conversely, when C-arm208 is in the lateral position, as in FIG. 43, the sensor bed 224 ispivoted to the vertical position such that the length and width of tiltsensor 14 are again perpendicular to gravity.

Coupler 260 may also include an integrated plumb line 274, which maygenerate a reference line viewable in fluoroscopic images generated byC-arm 208. Preferably, coupler 260 and plumb line 274 may be fixed tothe C-arm such that the plumb line 274 forms a vertical reference linein lateral fluoroscopic images. Plumb line 274 comprises an elongatedradio-dense marker 276 situated in a radio-opaque case 278. Case 278 isfixed to coupler 222 at a first end 280. A free end 282 may be attachedto C-arm face 258, via Velcro® or other suitable attachment means, tohelp prevent any movement of the plumb line 274 once it is positioned.

Coupler 260 is preferably fixed to the C-arm face 258 with the C-arm inthe lateral position, which allows gravity to help correctly positionthe plumb line 274. To attach coupler 260 to the signal receiver face258 according to a preferred embodiment, a Velcro® pad may be adhered tothe face 258 in a position 284 adjacent to the outer edge and centeredalong the vertical diameter of face 258. A complementary Velcro® pad maybe adhered to button 288 pivotally coupled to the bottom surface 286 ofcoupler 260 and the Velcro® pads stuck together. If it is not already inplace, tilt sensor 14 is positioned in sensor bed 224, which should beoriented in the vertical position (if C-arm is in the lateral position).The free end 282 of plumb line 274 may then be moved (e.g. via gravityof the user) such that plumb line 274 and coupler 260 pivot aroundbutton 288 until the tilt sensor is in the zero angle position. Once thezero-angle position is achieved, Velcro® pads may be used to attachanother button 290, situated on the free end 282 of plumb line 274, tothe face 258.

In addition to the vertical reference line for which plumb line 274 maybe utilized, other configurations are also contemplated. By way ofexample only, FIG. 44 depicts a target 292 which may be used with plumbline 274. Target 292 includes a generally circular radio-dense marker294 situated in a radio-opaque target case 296. Target case 296 includesan aperture slot 298 configured to receive and slidably engage case 278of plumb line 274. Once plumb line 274 is fixed in position, target 292may be slid along plumb line 274 until a desired position along plumbline 274 is achieved, after which it may be fixed in place with Velcro®or other suitable attachment means. FIG. 45 depicts target 292positioned along the plumb line 274 at the center of face 258. Circularradio-dense marker 294 has a diameter of approximately 1-inch. However,it will be understood that marker 294 may have any suitable size,ranging anywhere from just large enough to be seen, to just small enoughto fit on face 258 of receiver 214. It should also be understood thatwhile target marker 294 is shown and described as generally circular,target marker 294 may be provided having any general shape, includingbut not necessarily limited to, generally rectangular, triangular,ellipsoidal, and polygonal. In addition, plumb line 274 may alsocomprise various other configurations. With reference to FIG. 46, by wayof one example, case 278 may be shaped and dimensioned to approximatethat of receiver face 258, and radio-dense marker 276 may be providedaccording to any desirable layout, such as the four equal length barspositioned equidistantly around case 278 shown in FIG. 46.

While couplers 222 and 260 have been described as attaching the tiltsensor 14 in a pivotal relation, it should be appreciated that this isnot always necessary. In some instances (such as when determining thecranial-caudal angle using the C-arm) the sensor output is adequate ifonly one axis of the sensor is perpendicular to gravity. Thus the tiltsensor 14 may be engaged to the coupler in a fixed orientation.Alternatively, the need to pivot the tilt sensor 14 may be overcome byequipping sensor package 17 with a second 2-axis accelerometer arrangedperpendicular to the first. As the tilt sensor 14 is angled past theeffective range of the first accelerometer the second accelerometer takeover make assume the measurement function from the first accelerometer.

In an alternate embodiment of the present invention, it is contemplatedthat the orientation of C-arm 208 with respect to the patient 204 may beadjusted by moving the patient rather than the C-arm 208. To accomplishthis, by way of example only, trajectory system 10, and specifically,tilt sensor 14 may be attached to the surgical table 206. With the C-arm208 in the A/P position, the bed, and thus the patient on the bed, maybe rotated laterally (through a transverse plane), shown in FIG. 47, tochange the medial-lateral angle at which the x-ray beam 220 travelsthrough the patient. As shown in FIG. 48, the bed may also be rotated ina cranial or caudal direction (through a sagittal plane) to change thecranial-caudal angle at which the x-ray beam 220 travels through thepatient. The trajectory system 10, via feedback device 16, will displaythe cranial-caudal and medial-lateral angles of the bed with respect togravity. Since the beam 220 is parallel to the direction of gravity inthe A/P position, the cranial-caudal and medial-lateral angles oforientation of the x-ray beam with respect to the bed 206 (and patient204) are also known. To later obtain images from precisely the sameposition, the bed may be readjusted until the feedback device 16 againshows the angular readouts corresponding to the desired position.Although not shown, it is within the scope of the invention to attachthe tilt sensor 14 directly to the patient 204 rather than the bed 206.Again, with the C-arm 208 aligned in the A/P position, the bed may berotated to change one or both of the medial-lateral angle andcranial-caudal angle of the patient's spine with respect to the x-raybeam 218. Again, later images may be obtained from precisely the sameposition by readjusting the bed until the feedback device 16 again showsthe correct angular readouts for the position desired.

Simple and reproducible orienting of the C-arm 208 in a known positionwhile decreasing the x-ray exposure for everyone represents one generaladvantage of using the trajectory system 10 to enhance imagingtechniques during surgery. Other benefits may also be gained by usingthe system 10 with a C-arm, such as the previously mentioned benefit ofdetermining the angular orientation or trajectory of an anatomicalstructure within the patient. Without limiting the scope of the presentinvention, specific examples will be described for determining the axisof a vertebral pedicle, or in other words, the angles A1 and A2described above with regard to forming a pilot hole for pedicle screwimplantation.

In a first example, the trajectory system 10 equipped C-arm 208 may beused to help determine the axis of a pedicle as well as a good startingposition for entering the pedicle in line with the determined axis. Asmentioned, the implantation of pedicle screws without breaching,cracking, or otherwise compromising the pedicle wall is critical to thesuccess of a procedure still presents a significant challenge to spinalpractitioners. To mitigate this challenge according to one embodiment ofthe present invention, the orientation of the pedicle axis, defined by amedial-lateral angle A1 (illustrated in FIG. 49) and a cranial-caudalangle A2 (illustrated in FIG. 50), may be determined and the pediclescrew and/or related instruments may be advanced through the pediclealong the desired trajectory.

In this example the angle A1, or medial-lateral angle, of the pedicle isdetermined preoperatively in the same manner previously described withreference to FIG. 19. Specifically, a vertical reference line is drawnthrough the center of the vertebral body and a medial-lateral trajectoryline is drawn from a central position in the pedicle (e.g. a positionwithin the soft cancellous bone, as opposed to the harder cortical boneforming the outer perimeter of the pedicle) to an anterior point of thevertebral body. The angle formed between the medial-lateral trajectoryline and the vertical reference line is measured and represents theangle A1 value. The angle A2, or the cranial-caudal angle, maypreferably be determined intraoperatively with a C-arm fluoroscope 208equipped with the trajectory system 10 of the present invention. AngleA2 is determined in essentially the same fashion as it was describedpreviously. However, with the addition of the tilt sensor 14, need tomeasure the angle from the fluoroscopic imaging monitor is obviated.Instead, when the vertical reference line formed by plumb line 247 linesup with the pedicle, the pedicle angle A2 corresponds to the angle ofthe cranial-caudal trajectory angle of the C-arm tilt sensor 14, whichis displayed on feedback device 16.

To determine the cranial-caudal angle A2, the C-arm 208 is firstpositioned so that the base is perpendicular to the spine of the patient204. This may be verified with an A/P fluoroscopy image as shown in FIG.51. The base is perpendicular to the spine when the spinous process isequally spaced between the pedicles. Also, when the base of the C-arm208 is perpendicular to the spine, the vertical reference line createdby plumb line 274 is generally parallel to the vertebral endplates inthe A/P fluoroscopy image.

Once the alignment of the base is verified, the C-arm 208 is rotated tothe lateral position and the tilt sensor 14 may be pivoted into itscorresponding position (i.e. the horizontal position if the coupler isfixed to the receiver sidewall 256 or the vertical position if thecoupler is fixed to the receiver face 258). Starting from the lateralposition, illustrated in FIG. 52, the C-arm 208 may be rotated radially(through a sagittal plane) until the vertical reference line is parallelto the pedicle axis. In this position, which may be referred to as thetrajectory lateral position illustrated in FIG. 53, A2 is equal toA2(c). When the practitioner is satisfied with the alignment of thevertical reference line to the pedicle axis, the correct A2 valuemeasured from the tilt sensor 14 may be recorded from the feedbackdevice 16. Again, this angle measurement corresponds to thecranial-caudal angle A2 of the pedicle axis and the method may berepeated for each pedicle that is to receive a pedicle screw.

To select a starting point for pedicle penetration, the C-arm 208 may beplaced in the trajectory lateral position for the pedicle of interest.This may be accomplished by again lining up the vertical reference linein a lateral fluoroscopy image with the pedicle axis or by simplyrotating the C-arm until the tilt sensor 14 feedback readout 16indicates that the previously determined trajectory lateral position hasbeen attained (i.e. the angle measurement displayed by the tilt sensor14 matches the angle measurement displayed when the trajectory lateralposition was initially determined). From the trajectory lateralposition, the C-arm 208 may be rotated back to the A/P position whilemaintaining the rotation imparted to achieve the trajectory lateralposition. As pictured in FIG. 54, a pedicle penetration instrument, suchas instrument 12 described above, may be advanced to the target site andpositioned on the lateral margin of the pedicle, which is the preferredstarting point according to this example. The surgical instrument 12 maythen be oriented according to the medial-lateral and cranial-caudalangles previously determined (i.e. A1(i)=A1 and A2(i)=A2) and thereaftersafely advanced through the pedicle. The depth of penetration of thesurgical instrument 12 may be checked during advancement by rotating theC-arm back to a trajectory lateral view of FIG. 53. As pictured in FIG.55, the surgical instrument 12 should appear parallel to the verticalreference line in the trajectory lateral view.

An alternate method for determining a preferred starting point forpedicle penetration utilizes the “owl's eye” view described below.Specifically, the C-arm is oriented to the “owls eye” view, or in otherwords both the medial-lateral and cranial-caudal angles of the C-arm 208match the medial-lateral and cranial-caudal angles of the pedicle axis(A1(c)=A1 and A2(c)=A2). The tip of the pedicle access instrument 12 isplaced on the skin so that the tip is located in the center of thepedicle of interest on the fluoroscope image; this marks the preferredincision site. The access instrument 12 is advanced to the pedicle andanother fluoroscope image is taken to verify that the tip of theinstrument is still aligned in the center of the pedicle.

To orient the C-arm 208 in the owl's eye position, the medial-lateraland cranial-caudal angles of the pedicle axis may each be determined asdescribed with reference to FIGS. 21 and 51-53. Next, from thetrajectory lateral position, the C-arm is rotated back to the A/Pposition while maintaining the cranial-caudal orientation achieved inthe trajectory lateral position. Finally, while monitoring the feedbackdevice 16, the C-arm 208 is orbitally rotated until the angle matchesthe medial-lateral angle derived from the preoperative planning(A2(c)=A2). At this point the fluoroscopic image, illustrated in FIG.56, displays an “owl's eye” view of the pedicle, which appears generallyas a circle.

The owl's eye view illustrated in FIG. 56 may be utilized for variousreasons. By way of example, the owl's eye view may be used to determinethe starting point for penetration of the pedicle as described. Also, inthe owls eye image, a surgical instrument 12 properly aligned with thepedicle axis will appear as a black dot. Thus, once aligned, thesurgical instrument may be advanced through the pedicle while ensuringthat it continues to appear as only a dot on the fluoroscopy image. Thedepth of penetration may again be checked with a trajectory lateralimage (FIG. 55). Additionally, if preoperative planning was notconducted to determine angle A1 of the pedicle axis, the C-arm can bemanually (e.g. through trial and error) positioned in the owl's eyeview. Once the C-arm is positioned in the owls eye position the tiltsensor 14 may be read to determine the angle A1.

Still another example of the gainful application of the surgicaltrajectory monitoring system 10 to enhance surgical safety andefficiency includes monitoring the orientation of surgical accessinstruments. Monitoring trajectory can aid in both the insertion andpositioning of the access instruments themselves, as well as, aiding inthe later insertion of instruments and/or implants through the surgicalaccess instruments. One significant advantage is the ability to latervisually align surgical instruments and/or implants along the sametrajectory by visually comparing the alignment of the instrument to thatof the access instrument Often times during a surgical procedure, theorientation of a surgical instrument or implant is of critical import tothe success of the surgery. By way of example only, while placing bonescrews through a pedicle (which is a small generally tubular structureconnecting posterior elements of a vertebra to the vertebral body) it iscritical to ensure the screw is contained within the pedicle and doesnot breach the outer pedicle wall. Since the pedicle is surrounded bydelicate nervous tissue, a breach can have serious consequences for thepatient, ranging from mild pain to paralysis. One way to mitigate therisk of a pedicle breach during screw placement (including preparationfor screw placement, such as pilot hole formation and tapping) is todetermine the angular orientation of the pedicle and thereafter advancethe necessary instruments and screws along the determined trajectory. Byorienting the surgical access components along the pedicle trajectory,the surgical instruments and pedicle screws may be simply andefficiently advanced along the same trajectory, and thus avoid a breach,by “eyeballing” alignment with the access components.

An exemplary surgical access system 300 is described, by way of exampleonly, with reference to FIGS. 57-59. Surgical access system 300 includesa tissue distraction assembly 302 (FIG. 57) and a tissue retractionassembly 304 (FIG. 58) generally of the type shown and described incommonly assigned U.S. Pat. No. 7,207,949, the entire contents of whichis hereby incorporated in this disclosure as if set forth in itsentirety herein.

As shown in FIG. 57, the tissue distraction assembly 302 includes aK-wire 306, an initial dilating cannula 308, and a sequential dilationsystem 310. In use, the K-wire 306 is disposed within the initialdilating cannula 308 and the assembly is advanced through the tissuetowards the surgical target site (e.g. annulus). This is preferablyaccomplished while employing the nerve detection and/or directionfeatures described below. As will be described in detail below, dilationmay also be carried out along a desired angular trajectory path by usingthe surgical trajectory system 10 of the present invention. After theinitial dilating assembly is advanced such that the distal end of theinitial dilator 308 is positioned within the disc space, the sequentialdilation system 310 consisting of one or more supplemental dilators 312,314 may be employed for the purpose of further dilating the tissue downto the surgical target site. Each component of the sequential dilationsystem 310 (namely, the K-wire 306 and the supplemental dilators 312,314) may, according to the present invention, be provided with one ormore electrodes (preferably at their distal regions) equipped for usewith a nerve surveillance system, such as, by way of example, the typeassociated with the neuromonitoring system 400 discussed below.

As shown in FIG. 58, the retraction assembly 304 includes a plurality ofretractor blades extending from a handle assembly 334. By way of exampleonly, the handle assembly 334 is provided with a first retractor blade336, a second retractor blade 338, and a third retractor blade 340.Although shown and described below with regard to the three-bladedconfiguration, it is to be readily appreciated that the number ofretractor blades may be increased or decreased without departing fromthe scope of the present invention. The retractor assembly 304 is shownin a fully retracted or “open” configuration, with the retractor blades336, 338, 340 positioned a distance from one another so as to form anoperative corridor 348 there between and extending to a surgical targetsite (e.g. an intervertebral disc). As will be described in detailbelow, the placement of the retraction assembly 304 may be carried outalong a desired angular trajectory path by using the surgical trajectorysystem 10 of the present invention. Each component of the retractionsystem 304 (namely, the blades 336-340) may, according to the presentinvention, be provided with one or more electrodes (preferably at theirdistal regions) equipped for use with a nerve surveillance system, suchas, by way of example, the type associated with the neuromonitoringsystem 400 discussed below.

To use the angle monitoring system 10 with the surgical access system300, the desired trajectory of the surgical corridor may be determined.If for example, the surgeon intends to implant pedicle screws throughthe resulting operative corridor 348, it may be desirous to orient thesurgical corridor 348 along the pedicle axis. Methods for determiningthe pedicle axis have been described previously and may be followed hereagain to obtain the desired angle values.

Once the pedicle trajectories have been determined the practitioner maybegin advancing the surgical access system 300 according to the desiredangular trajectory. The K-wire 306 is advanced into the pedicle. If arigid K-wire is utilized the tilt sensor 14 may be attached to aproximal end of the K-wire 306 via universal clip 26, and the angle ofinsertion guided by the feedback device 16. After the K-wire 306 isdocked in the vertebra, the clip 26 is removed (if it was used) and maybe attached to the first dilator 308 for insertion, again following thedesired trajectory via the feedback device 16. This is repeated untilthe last dilator 310 is in place over the surgical target site. Next,the tilt sensor 14 may be removed from the final dilator and attached tothe retractor 304 and as previously described, the surgical retractorassembly 304 may be advanced to the target site over the outer dilatorwith the blades 336, 338, 340 in the “closed” position. The dilator isremoved and the blades may be retracted to an “open” position providinga corridor 348 for the surgeon to work. If the angle of the retractor304 was not determined during insertion it may be determined at thispoint by attaching the tilt sensor 14 in the manner described and thenreading the measurements.

After the retractor assembly 304 is set in the proper angular alignment,a pilot hole may be formed in the pedicle. By way of example only a gearshift probe or awl may be advanced to the pedicle. Once the tip of theinstrument rests on the pedicle the shaft of the instrument should beadjusted until it is aligned both medial-laterally and cranial-caudallywith the axis of the first retractor blade 336. When aligned with theaxis of the first blade, or in other words, with the longitudinal axisof the surgical corridor, the instrument tip may be driven into thepedicle along the pedicle axis, ensuring that the pedicle wall is notbreached. This may be repeated for a tapping instrument and during screwinsertion. After the first screw is inserted along the pedicle axis, theretractor system 304 may be adjusted until it is aligned with the axisof the next pedicle to receive a screw, and the steps are repeated againuntil the next screw is placed. Once every screw has been placed andconnecting elements inserted and locked into the screws, the retractorsystem 304 may be removed. It will again be appreciated that althoughthis method is described as orienting the retractor assembly along apedicle axis and thereafter inserting instruments into the pedicle,there are any number of procedures which may be benefited by insertingan instrument along a specific trajectory and the method describedapplies equally thereto.

Coupling the tilt sensor 14 to the various components of the distractionassembly 302 and retraction assembly 304 may be accomplished in any of avariety of manners. With reference to FIG. 60, the universal clip 26(and thus tilt sensor 14) may be attached to one of the sequentialdilators 310. In the same fashion as described above in relation to thepedicle access probe, a portion of the surgical distraction component,preferably near the proximal end, is positioned within the hook of freeend 54 of clip 26. Collar 34 may then be twisted to securely fasten thedistraction component to the universal clip 26. When completelyfastened, the tilt sensor 14 extends perpendicularly to the longitudinalaxis of the distraction component. Since the component is angled ineither of the sagittal or transverse planes, the user may be apprised ofthe angle relative to gravity via feedback device 16. It will beappreciated that while the tilt sensor 14 is shown in FIG. 60 attachedonly to the outer or largest dilator, the clip may be attached to theK-wire and then each dilator in turn if desired.

With reference to FIGS. 61-63, the universal clip 26 (and thus the tiltsensor 14) may be attached to the tissue retractor assembly 304. In FIG.61, the universal clip 26 is attached to a post 312 extending verticallyfrom the top of first retractor blade 336. This embodiment isadvantageous in that the post 312 may be in electrical communicationwith an electrode 350 at or near the distal end of retractor blade 336.The universal clip 26 may be in electrical communication with aneuromonitoring system 400, described below, such that electricalstimulations from the neuromonitoring system 400 may thus be deliveredthrough the universal clip 26, eliminating the need for connectingmultiple devices to the retractor 304. In FIG. 65, the universal clip 26is attached to a post 313 used to attach the surgical retractor assembly304 to an articulating arm 315 which provides secure connection to theoperating table and holds the retractor assembly in place.

Whether universal clip 26 is attached to post 312 (as in FIG. 61) orpost 313 (as in FIG. 62) it will be appreciated that it extendsperpendicular to the longitudinal axis of the surgical corridor 348created between the retractor blades. It will be appreciated that, ifand when the second and third retractor blades 338, 340 are rotated outduring surgery, the longitudinal axis of the surgical corridor remainsthe same and follows the axis of the first blade 336 which does notrotate. It should also be appreciated that though the clip 26 is shownin FIGS. 61 and 62 extending over the retractor blades and the corridor348 they create, this is done for the ease of viewing and preferably thesurgical trajectory assembly 10 is oriented such that the clip 26extends away from the surgical corridor when so as not to inhibit thesurgeons ability to manipulate instruments and/or see the surgicalwound.

FIG. 63 shows a tissue retractor connected directly to the handleassembly 334 of a tissue retractor 304 via any number of suitablemanners, including but not limited to the use of a Velcro® patch, tape,strap, etc. . . . The tilt sensor 14 is preferably positioned on thehandle assembly 334 such that it is perpendicular to the longitudinalaxis of the spine, thus as it is shown in FIG. 63, the handle extensionswould face out to the side of the patient, perpendicular to thelongitudinal axis of the spine. If necessary, the tilt sensor may bedetached and repositioned.

In addition to being physically coupled to the retractor 304, it will beappreciated that the tilt sensor 14 may be formed as an integral part ofthe retractor 304 and/or any individual component thereof withoutdeparting from the scope of the present invention. For example, the tiltsensor 14 may be formed as part of any of the retractor blades 336, 338,340, any component of the handle assembly 334, and/or any component ofthe dilation assembly 302. In such an instance, the “tilt-sensor enabledcomponent” may be have an electrical coupling and/or wirelesscommunication technology to provide the tilt sensing functionalitydescribed herein and may be disposable or reusable as described herein.

The surgical trajectory system 10 described above may be used incombination with any number of neurophysiologic monitoring systems.These may include, but are not necessarily limited to, neurophysiologicmonitoring system capable of conducting pedicle integrity assessmentsbefore, during, and after pilot hole formation, as well as to detect theproximity of nerves while advancing and withdrawing the surgicalinstrument (e.g. probe 12, awl 80, dilation assembly 302, retractionassembly 304) from the pedicle target site. An exemplary neuromonitoringsystem 400 is shown by way of example in FIG. 64. Neuromonitoring system400 has been described in detail elsewhere and will be described onlybriefly herein. By way of example only, the various functional modes ofthe neuromonitoring system 10 may include the Twitch Test, Free-run EMG,Basic Screw Test, Difference Screw Test, Dynamic Screw Test, MaXcess®Detection, and Nerve Retractor, all of which will be described brieflybelow. The Twitch Test mode is designed to assess the neuromuscularpathway via the so-called “train-of-four test” test to ensure theneuromuscular pathway is free from muscle relaxants prior to performingneurophysiology-based testing, such as bone integrity (e.g. pedicle)testing, nerve detection, and nerve retraction. This is described ingreater detail within Int'l Patent App. No. PCT/US2005/036089, entitled“System and Methods for Assessing the Neuromuscular Pathway Prior toNerve Testing,” filed Oct. 7, 2005, the entire contents of which ishereby incorporated by reference as if set forth fully herein. The BasicScrew Test, Difference Screw Test, and Dynamic Screw Test modes aredesigned to assess the integrity of bone (e.g. pedicle) during allaspects of pilot hole formation (e.g., via an awl), pilot holepreparation (e.g. via a tap), and screw introduction (during and after).These modes are described in greater detail in Int'l Patent App. No.PCT/US02/35047 entitled “System and Methods for Performing PercutaneousPedicle Integrity Assessments,” filed on Oct. 30, 2002, andPCT/US2004/025550, entitled “System and Methods for Performing DynamicPedicle Integrity Assessments,” filed on Aug. 5, 2004 the entirecontents of which are both hereby incorporated by reference as if setforth fully herein. The MaXcess® Detection mode is designed to detectthe presence of nerves during the use of the various surgical accessinstruments of the neuromonitoring system 10, including the k-wire 62,dilator 64, cannula 66, retractor assembly 70. This mode is described ingreater detail within Int'l Patent App. No PCT/US02/22247, entitled“System and Methods for Determining Nerve Proximity, Direction, andPathology During Surgery,” filed on Jul. 11, 2002, the entire contentsof which is hereby incorporated by reference as if set forth fullyherein. The Nerve Retractor mode is designed to assess the health orpathology of a nerve before, during, and after retraction of the nerveduring a surgical procedure. This mode is described in greater detailwithin Int'l Patent App. No. PCT/US02/30617, entitled “System andMethods for Performing Surgical Procedures and Assessments,” filed onSep. 25, 2002, the entire contents of which are hereby incorporated byreference as if set forth fully herein. Although not described herein,various other functional modes may be performed by the system 10, suchas for example only, MEP and SSEP functions which are described indetail within Int'l Patent App. No. PCT/US2006/003966, entitled “Systemand Methods for Performing Neurophysiologic Assessments During SpineSurgery,” filed on Feb. 2, 2006, the entire contents of which are herebyincorporated by reference as if set forth fully herein.

With reference to FIG. 64, the neurophysiology system 400 includes adisplay 401, a control unit 402, a patient module 404, an EMG harness406, including eight pairs of EMG electrodes 408 and a return electrode410 coupled to the patient module 404, and a host of surgicalaccessories 412, including an electric coupling device 414 capable ofbeing coupled to the patient module 404 via one or more accessory cables416. As shown in FIGS. 65-66, to perform the neurophysiologicmonitoring, the surgical instrument 12, 80 is configured to transmit astimulation signal from the neurophysiology system 400 to the targetbody tissue (e.g. the pedicle). As previously mentioned, the probemembers 60, 82 may be formed of material capable of conducting theelectric signal. To prevent shunting of the stimulation signal, theprobe members 60, 82 may be insulated. By way of example, a substantialportion of probe members 60, 82 may be provided with an insulativecoating. Uninsulated portions near the distal end 90 form a stimulationregion (or “electrode”) 135. An additional uninsulated region is alsoprovided near the proximal end of the probe member to serve as acoupling point 137 for linking the neurophysiology system to theinstrument 80. In another embodiment, not shown, a retractableinsulative sheath, as described in U.S. patent application Ser. No.11/448,237, may be employed in place of, or in addition to theinsulative coating. In still another alternative, probe members 60, 82may be formed of a non-conductive material with one or more embeddedconductive elements at or near the distal end capable of beingcommunicatively linked with neurophysiology system 400.

The neurophysiology system 400 performs nerve monitoring during surgeryby measuring the degree of communication between a stimulation signaland nerves or nerve roots situated near the stimulation site. To dothis, the surgical instrument is connected to the neurophysiologymonitoring system 400 and stimulation signals are activated and emittedfrom electrode 135. EMG electrodes 408 positioned over the appropriatemuscles measure EMG responses corresponding to the stimulation signals.The relationship between the EMG responses and the stimulation signalsare then analyzed by the system 400 and the results are conveyed to thepractitioner on the display 401. More specifically, the system 400determines a threshold current level at which an evoked muscle responseis generated (i.e. the lowest stimulation current that elicits apredetermined muscle response). Generally the closer the electrode 135is to a nerve the lower the stimulation threshold will be. Thus, as theprobe member 60, 82, or surgical access members 302, 304 move closer toa nerve, the stimulation threshold will decrease, which may becommunicated to the practitioner to alert him or her to the presence ofa nerve. The pedicle integrity test, meanwhile, works on the underlyingtheory that given the insulating character of bone, a higher stimulationcurrent is required to evoke an EMG response when the stimulation signalis applied to an intact pedicle, as opposed to a breached pedicle. Thus,if EMG responses are evoked by stimulation currents lower than apredetermined safe level, the surgeon may be alerted to a possiblebreach.

The surgical instrument 12, 80, 302, 304 may be connected to theneurophysiology system 400 by attaching a DIN cable 413 to thereceptacle 50 of universal clip 26. When tilt sensor 14 is attacheddirectly to the surgical instrument (rather than using universal clip26), as with instrument 80 described above, an electric coupling device414 may be provided with the neurophysiology system 400. The electriccoupling device may be attached to the uninsulated coupling point 137 atthe proximal end 64 of probe member 82. The electric coupling device 414may comprise a number of possible embodiments which permit the system400 to attach to the coupling point 137 and transmit a stimulationsignal through the probe member 82.

One such embodiment of electric coupling device 414 utilizes aspring-loaded plunger to hold the coupling point 38 and transmit thestimulation signal. The plunger 418 is composed of a conductive materialsuch as metal. A nonconductive housing 414 partially encases the plungerrod 418 about its center. Extending from the housing 420 is an end plate424. An electrical cable 426 connects the electric coupling device 414to neurophysiology system 400. A spring (not shown) is disposed withinthe housing 420 such that in a natural or “closed” state the plunger 418is situated in close proximity to the endplate 424. Exerting acompressive force on the spring (such as by pulling the cable 426 whileholding the housing 420) causes a gap between the end plate 424 and theplunger 418 to widen to an “open” position, thereby allowing insertionof the coupling point 137 between the end plate 424 and plunger 418.Releasing the cable 426 allows the spring to return to a “closed”position, causing the plunger 418 to move laterally back towards theendplate such that a force is exerted upon the coupling point 137 andthereby holds it in place between the endplate 424 and the plunger 418.Thereafter, the electrical stimulus may be passed from theneurophysiology system 400 through the cable 426 and plunger 418 to theprobe member 82.

Alternatively, the electrical coupling device may be embodied in theform of a clip 428. The clip 428 is comprised of two prongs hingedlycoupled at a coupling point 430 such that the clip 428 includes anattachment end 432 and a non-attachment end 434. A stimulation electrode436 is disposed on the attachment end 432 and communicates with anelectric cable 426 extending from the non-attachment end 434 to theneurophysiology system 400. In a “closed” position the prong ends at theattachment end 432 touch. Depressing the prongs at the non-attachmentend 434 in a direction towards each other causes a gap to form betweenthe prong ends at the attachment end 432. Positioning the “opened”attachment end 432 over the coupling point 137 and releasing the forceon the non-attachment end 434 causes the attachment end 432 to pinchtight on the coupling point 137 and thereby allow the electricalstimulus to pass from neurophysiology system 400, through thestimulation electrode 236, to the probe member 82.

During pilot hole formation, while the trajectory of the surgicalinstrument is being monitored to prevent the instrument from breachingthe pedicle walls, pedicle integrity assessments may be performed toalert the practitioner in the event a breach does occur. Stimulationsignals are emitted from electrode 135, which should be at leastpartially positioned within the pedicle bone during hole formation. Thestimulation threshold is determined and displayed to the surgeon via theneurophysiology monitoring system 400. Due to the insulatingcharacteristics of bone, in the absence of a breach in the pedicle wall,the stimulation threshold current level should remain higher than apredetermined safe level. In the event the threshold level falls belowthe safe level, the surgeon is alerted to the potential breach. When thepilot hole is fully formed, a final integrity test should be completed.

In one embodiment, tilt sensor 14 is communicatively linked directly tocontrol unit 402 of the neurophysiology monitoring system. The display401 of neurophysiology system 400 replaces feedback device 16 of thetrajectory monitoring system 10 and data from the tilt sensor 14 isshown jointly with the neurophysiologic data. As described above, audioindicia may also be communicated to the user regarding the trajectoryangles.

The systems and methods described above may be utilized by personnelduring surgical procedures to help maximize efficiency and increasesafety. Each of the applications for, and methods of, using the surgicaltrajectory system 10 described above have advantages when used on theirown and it is expressly noted that combining some or all of thedifferent uses and methods of the trajectory system may be especiallybeneficial. By way of example only, a trajectory assisted method andprocedure for pedicle fixation utilizing multiple aspects of thetrajectory system 10 will now be described.

The trajectory assisted pedicle fixation procedure begins with theproper positioning of the patient 204. The patient is positioned on thesurgical table 206 in the prone position and the affected spinal levelsare adjusted until they are level with the floor. Once the patient ispresumed to be properly positioned, one or more of a visual inspection,A/P fluorography, and a mechanical inspection with a level may beperformed to verify the position.

After positioning of the patient 204 is complete the angles to be usedfor pilot hole formation may be determined. The first angles to bedetermined are the medial-lateral angles A1. As previously noted thisstep can be completed prior to the surgery and the medial-lateral anglesfor each pedicle to receive a screw are brought into the operating roomfor reference. To calculate the medial-lateral angle A1, the pedicleangle correction value should be determined (and loaded into CPU or theneuromonitoring system 400 if applicable), if necessary, by firstdetermining the amount of rotation in the spine relative to the verticalreference in the MRI or CAT image. The angular difference between a linedrawn connecting the posterior superior iliac spine (PSIS) and the lineparallel to the bottom of MRI image box. Next, a line is drawn down thepedicle axis of each pedicle and a vertical reference line is drawnbetween them through the center of the vertebral body. A measuringdevice, such as a protractor may then be used to calculate the angulardifference between the vertical reference line and the lines drawnthrough the axis of the pedicles. The values determined are themedial-lateral angles to use for pedicle cannulation during pilot holeformation. The step is repeated until the medial-lateral angle for eachpedicle of interest is determined. Again if necessary, correct the anglevalues determined based on the pedicle angle correction value.

After determining the medial-lateral angles for each pedicle, the nextstep is to obtain the cranial-caudal angles A2 for each pedicle as well.The superior endplate is positioned parallel to the reticle plumb line274. The angle of the pedicle axis is (or vertebral endplate) ismeasured relative to the C-arm gravity line. This is accomplished byfirst placing the C-arm 208 into the lateral orientation. The reticleline represents the gravity line and all cranial-caudal angles aremeasured relative to this reference line. The head or foot of thesurgical table 206 may be raised or lowered to attain parallel alignmentbetween the superior endplate of applicable vertebral body and thisreference line, if desired.

The cranial and caudal angles of applicable pedicle axes or superiorendplates are measured via one of two methods. First, a protractor 120outfitted with a tilt sensor 14 may be lined up with the verticalreference line formed by the plumb line 274 and zeroed. Subsequently,the protractor 120 is rotated into alignment with the pedicle axis ordesired trajectory. Subsequent angles are measured per vertebral levelusing the same method.

In the second method, the plumb/reticle line 274 and the associated tiltsensor 14 is utilized to measure the angles. The C-arm 208 is rotated inradial rotation until the plumb line 274 parallel to the pedicle axis orsuperior endplate of interest and the angle is noted. Then the plumbline 274 is rotated parallel to the superior endplate of the upper levelvertebra and the angle is noted. The resulting cranial caudal angles arerecorded and are used to facilitate later positioning of the C-arm intothe A/P plane of the vertebra of interest.

The next main step of the trajectory assisted pedicle fixation procedureof the preset invention is to properly position the C-arm 208. Initiallyall the C-arm articulations are set to zero and the horizontal arm isset at midline. Next the C-arm radial rotation is set to thepredetermined cranial-caudal angle A2 for the level of interest. TheC-arm base is then translated cranially or caudally to align theplumb/reticle reference line 274 parallel to the superior endplate ofthe vertebral body of interest. Then the orbital rotation of the C-armis altered slowly until the C-arm angle A1(c) matches the predeterminedmedial-lateral angle A1. Finally, the C-arm is translated usinghorizontal arm translation to center beam 218 over the right lower levelpedicle.

Next the starting point for pedicle cannulation is determined. A tiltsensor 14 is attached to the pedicle access instrument 12. The tip ofthe instrument 12 is placed on the skin so that the tip is located inthe center of the pedicle and the location is marked with a pen. Using ascalpel a longitudinal 1.5 cm incision centered over the pen mark ismade.

The instrument 12 is advanced oriented in the same owl's eye trajectory,through the incision all the way to the bone. A C-arm 208 image is usedto see if the tip of the needle is near the axis of the pedicle. If notthe tip is adjusted until it is directly in the center of the lowerlevel pedicle.

The surgical instrument 12 is attached to the neuromonitoring system 400and via the one of a coupling device 414 and DIN cable 413. Onceneuromonitoring capability is established the instrument is advanced toa depth of 1 cm and medial wall integrity is confirmed with a C-arm 208shot at the 1 cm point. The instrument may be advanced while making anyadjustments necessary to keep the trajectory in line with the pedicleaxis. A final C-arm 208 shot may be taken at the final position forconfirmation. After pedicle cannulation is performed on the right sideof the lower level, the steps may be repeated again on the left side.

To move on to adjacent levels, owl's eye views may be obtained fromprevious levels by C-arm articulations and x-ray image sequencesaccording to the following: first orient the C-arm by radial rotation tothe upper level specific cranial-caudal angle; align the target levelsuperior endplate with the reticle/plumb line 274 by C-arm basetranslation; next orient the C-arm by orbital rotation to specificmedial-lateral angle; then translate the C-arm horizontal armtranslation to center the pedicle of interest in the image; and finally,cannulate the pedicle. These steps are repeated until all pedicles havebeen cannulated. Implantation of the pedicle screws and supporting rodsmay now be implanted, preferably using a lateral fluoroscopy view.

While the invention is susceptible to various modifications andalternative forms, (such as the drill bit, needle points, and T-handlementioned above) specific embodiments thereof have been shown by way ofexample in the drawings and are herein described in detail. It should beunderstood, however, that the description herein of specific embodimentsis not intended to limit the invention to the particular formsdisclosed, but on the contrary, the invention is to cover allmodifications, equivalents, and alternatives falling within the scopeand spirit of the invention as defined herein. By way of example, themethod for determining the cranial-caudal A2 has been described hereinas taking place intraoperatively using lateral fluoroscopy imaging.However, the cranial-caudal angle may also be determined preoperativelyemploying various imaging and/or computer processing applications. Forexample, a 3-D model of a patient's vertebra (or other applicable bodypart) may be obtained using a combination of medical imaging andcomputer processing. From the 3-D model the angle A2 may be calculatedafter which the determined value may be utilized by the surgicaltrajectory system and methods described above. It is furthercontemplated that computer processing of medical images may be used toextrapolate the pedicle axis angles A1 and A2 without the need for humanintervention. Finally, it will be appreciated that the intraoperativemonitoring discussed herein has generally focused on the use of a C-armfluoroscopic imager, however, orienting the C-arm with a tilt sensor andproviding a trajectory oriented reticle/plumb line using the methods andsystems described herein may apply to any form of intraoperativemonitoring.

1. A system for controlling the trajectory of a surgical instrument,comprising: an orientation sensor coupled to said surgical instrumentand operable to determine a first angular relationship in a first planebetween said sensor and a reference direction and operable to determinea second angular relationship in a second plane between said sensor andsaid reference direction, wherein said second plane is orthogonal tosaid first plane and said sensor is coupled to said surgical instrumentin a known orientation; and a feedback device communicatively coupled tosaid sensor and configured to communicate information to a userregarding at least one of said determined first and second angularrelationships between said sensor and said reference direction.